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Waterway and wetland permits: part II - management of aquatic plants and algae in ponds

Maintaining a pond

Ponds will grow abundant populations of plants and algae unless you can reduce sediment and nutrient runoff into your pond. A buffer strip of native vegetation around the pond will help trap soil and nutrients before they enter the water. As a general rule, the larger the buffer the more effective it will be. A minimum of 35 feet is recommended. Many experts recommend 150-foot buffers or more if you have the room. Clearing a small area can provide you with a place to access your pond, relax and observe wildlife at the same time.

As a general rule, the larger the buffer, the more effective it will be; however, a minimum of 35 feet is recommended.

A pond with a buffer strip of trees and native plants surrounding it can become the perfect home for a variety of birds and animals. The deeper the buffer the better for songbirds, ducks, amphibians and other creatures. Some literature suggests that a buffer strip will reduce the potential for geese to populate the area. Geese tend to shy away from thick vegetation that may hide predators.

Keeping fertilizer and animal wastes out of your pond is vital. These nutrients can trigger excessive plant and/or algae growth. Avoid fertilizer use (or use zero phosphorus fertilizer such as 18-0-5) around the pond and keep livestock out of the pond basin. Last, but not least, protect wetland areas during and after pond construction by not filling or disturbing them before. Implementing these practices early on will reduce the need for costly management in the future.

Plants happen

You generally do not have a lot of control over the types of plants that will appear in your pond except for those you purposely plant. Mother Nature has figured out some nifty ways of bringing algae and plants to your pond. Algae are very common organisms that can be found on land as well as in water. They are often the first occupants of your pond; aquatic plants come later. Seeds and fragments are brought in by the wind, on the feet of waterfowl, or tucked within the tufts of fur-bearing animals. Henry David Thoreau once remarked on this phenomenon by stating, "You will no sooner have your pond dug than nature will begin to stock it." Plants and algae, invited or not, will eventually find their way to your pond.

You will no sooner have your pond dug than nature will begin to stock it.

Maintaining a healthy balance of aquatic plants is critical to a pond's ecosystem. Aquatic plants provide the basic resources for the rest of the pond community including oxygen production, spawning and nesting habitat, and food resources. Additionally, aquatic plants act to stabilize sediments and tie up excess nutrients. Therefore, it is rarely desirable to remove all the plants from a pond.

If you are considering transplanting aquatic plants from another waterbody, please check with your local DNR Service Center first. Make sure you know what you are planting. Certain aquatic plants may be considered highly valuable, or even rare or endangered, and should not be gathered. Other plants (such as purple loosestrife and Eurasian water milfoil may be detrimental to your pond environment, and your pond could be a source for infestation of nearby waters.

The toolbox for plant and algae control

Once you have determined the objectives for your pond, the next step is to examine the assortment of management tools available to achieve your goals. These tools range from very intensive and costly reclamation techniques to low-cost, annual maintenance methods. Management strategies are often identified with one of four general categories: chemical, mechanical, physical and biological. A factsheet available from the DNR titled "Aquatic Plant Management and Protection Program" [Publication # PUB-WR-448] provides greater details about the regulations and permitting requirements.

Chemical management methods

Among the chemical tools available for pond management are herbicides, water colorants and nutrient inactivation compounds. Aquatic chemicals include herbicides (that control plants), algaecides (that control algae), insecticides (that control mosquitoes and other insects) and piscicides (that control fish). Water colorants are usually blue dyes. Nutrient inactivation compounds are chemicals such as aluminum sulfate (alum), calcium bicarbonate (limestone) as well as some iron compounds.

Water colorants

Men in Motorboat Adding Dye to Pond

A number of different water colorants or dyes are widely available. The dyes are generally blue and are designed to reduce the amount of light penetrating the surface of a pond, thereby reducing plant and algae growth. The dyes are usually non-toxic, water-soluble and degrade over a period of weeks. Permits are required for the use of dyes that have United States Environmental Protection Agency (USEPA) registration numbers. Dyes that do not claim to control plants or algae have not been required to complete the USEPA toxicity testing or product registration. Dyes may reduce the need for other management strategies but are usually not a "cure-all." If your pond has an occasional outflow, it will be difficult to use a dye without discharging the colored water downstream causing complaints and possibly resulting in enforcement actions.

Nutrient inactivation

Aluminum sulfate or alum is used in lakes to precipitate phosphorus from the water column and reduce its release from bottom sediments. Pond sediments treated with alum may release fewer nutrients and prevent excessive algae blooms. Alum will not affect the growth of aquatic plants in your pond except for reducing algae and improving water clarity, thereby improving conditions for aquatic plant growth. Alum will not bind to new phosphorus entering the pond; therefore it is wise to reduce nutrient inputs before treating the pond. The application of alum involves calculations based upon the pH, hardness and water volume. It is recommended that a professional pond management firm be consulted prior to using alum. DNR approval for the application of alum to a pond may be required if there is a potential for discharge of the chemical or your pond is considered a public waterway. Check with your local DNR Service Center.

Barley straw

Recent studies have shown that bales of barley straw submerged in the pond and around the pond's perimeter can reduce the occurrence of algae. This method seems to be most effective when used prior to large accumulations of algae as it does not kill algae that are already present. This might be something to try on small, private ponds, but would not be a suitable technique for ponds with considerable outflow or where the straw bales interfere with navigation, shore fishing or swimming.

Mechanical management methods

Harvesting

Mechanical methods available for pond plant management include harvesting, and dredging. Small-scale mechanical harvesting on ponds can be an effective management tool. A variety of hand-held or boat mounted cutters are available from private firms. Removing the cut plants will help take nutrients out of the pond and limit algae growth. Although plant parts are usually an insignificant amount of nutrients compared to annual runoff or groundwater inputs, removing as much of the cut plants as possible is best for your pond. A factsheet available from the University of Wisconsin-Extension [exit DNR] titled "Your harvesting program" [Publication # PUB-FH-205-97] provides detailed information about operating a large lake harvesting program but has some useful information that you may find applicable to your small private ponds.

Dredging

Dredging is an expensive and intensive pond management technique that can substantially change the condition of your pond. Dredging can be used in constructing, maintaining and restoring ponds. Make sure you have a detailed plan agreed on by you and your contractor prior to starting a dredging project.

Dredging of your pond may require permits from the DNR, ACOE and your local unit of government. ALWAYS CHECK FIRST!

You will generally need a Chapter 30 dredging permit from the DNR if:

  • Your pond is a naturally existing pond or wetland.
  • Your pond is connected to or is within 500 feet of a navigable waterway (stream, river or lake).
  • Your pond is fed from a stream, from a lake or from a high capacity well.
  • You plan on excavating or working in a floodplain, wetland or shoreland zone.

Dredging helps to control aquatic plants in two ways:

  • By removing the soft, nutrient rich sediment that has built up on the bottom of the pond.
  • By deepening the pond to the extent that light is not available for plant growth (generally greater than 10 or 15 feet depending on water clarity).

Dredging may or may not help reduce an algae problem. If your pond has a firm bottom of sand, gravel, clay or bedrock, dredging the soft muck on top may provide you with greater depth, reduced nutrients for algae, and more oxygen. However, if the pond is without a firm bottom, dredging will only deepen the pond and may even increase algae or aquatic plant problems by exposing bottom sediments that contain more available nutrients. Permit applications for dredging are often denied especially if it is a mapped wetland.

Dredged material from your pond must be disposed of in an upland site, except for the approved construction of berms for wildlife ponds. Sediment disposal may also require a DNR Solid Waste Permit if dredged volumes exceed 3,000 cubic yards or if the sediment is classified as hazardous. Proper erosion control measures are needed to protect nearby wetlands, lakes, streams or your pond itself. As part of the DNR permitting process you may need to have the sediments tested to identify any contamination problems and avoid environmental and liability problems during dredging or after disposal of the material. Conventional dredging operations utilize a multitude of techniques such as draglines, backhoes, front-end loaders, bulldozers and dump trucks to dig out the bottom sediments. Hydraulic dredging uses pumps and hoses (that may have an attached cutter head) to pump the bottom material to containment areas. The material may have to "de-water" within the containment area for weeks or months before the site can be restored by grading and planting vegetation. Discharges of water from dredged sediment to either the groundwater or surface water may require a WPDES permit. More information about dredging and permit requirements is detailed in the DNR factsheet "Waterway permits for dredging projects" [Publication # PUB-FH-058].

Physical management methods

Management techniques that change the physical characteristics of the pond include raking, aeration, bottom fabrics, sand blankets and drawdown. All of these physical management techniques, with the exception of raking, may require DNR permitting or approval. Check with your local DNR Service Center prior to implementing these projects.

Raking

Good old-fashioned raking is perhaps the most cost-effective method of removing excess aquatic plants from a pond. Many homemade gadgets have been invented to achieve this purpose. These include everything from modified garden rakes to bedsprings to welded sickle bars that can be dragged across the pond's bottom in an effort to cut and uproot aquatic vegetation. There are also a variety of tools that are marketed and can be purchased through private vendors. Perhaps the greatest advantage to raking is that it allows you to remove plant material along with their stored nutrients. This can help to reduce the potential for nuisance conditions in the future. A secondary advantage of raking is that you are also reducing the chance for oxygen depletion caused by plant decomposition. The drawback to raking is that it may be very labor intensive depending on the size and depth of your pond as well as the extent of aquatic plant growth.

Cut plant fragments must be removed from the water. Fragments of certain plants can re-root and form new beds of plants, compounding the problem. If the harvested plants are not removed, they add nutrients to the water as they decompose and fertilize the other plants in the pond. Decomposing plant fragments can deplete dissolved oxygen in the water. Harvested plants should be piled far away from the shore to prevent nutrients from leaching back into the pond. After the plants are allowed to dry they can be composted or mulched. Harvested aquatic plants should not be hauled to the local landfill. Check to see if your community has a compost site that will allow aquatic plants.

Aeration

Fountain in a Pond

Fountains, bubblers or air injection aeration units are used to increase the amount of dissolved oxygen in the water. This technique may reduce the recycling of nutrients from the sediments. This makes the nutrients unavailable for algae growth or free floating plants like duckweed. Air injection and bubbler aeration units increase turbulence within your pond, which may also reduce algae or duckweed growth. If your pond bottom is very silty, be careful that your aeration unit is not continuously re-suspending bottom sediments. In practicality, aeration may not solve your algae problem and has no effect on plant growth. But it may reduce the need for other algae control methods. Aeration units are usually installed based on ? horsepower to 1 horsepower per acre of water and can cost a few hundred dollars for a basic bubble compressor type to thousands of dollars for a fountain with synchronized lights and spray patterns. Permits are required for the aeration of public ponds and lakes, but not in private ponds.

Bottom barriers

Bottom barriers are constructed from a variety of materials including polyvinyl chloride (PVC) liners, coated fiberglass mesh screen and other materials. Sheets of these fabrics are anchored to the pond bottom. All plants beneath the fabric are controlled with the exception of free-floating plants and algae. In some cases, bottom fabrics are used to provide a more favorable swimming area. These types of barriers can interfere with fish spawning and other pond wildlife. Over time, barriers may require maintenance due to siltation, ice damage, bubbling up and normal wear and tear. Barriers are usually sold on a square foot basis and range from $0.20/sq. foot for the material to $1.00 or more, including professional installation. Although they cost more initially, they can last 5 to 10 years and are useful for pond areas near small piers and beaches. Like aerators, permits are required on public lakes and streams, but no permits are required to install bottom barriers in private ponds.

Readying a bottom barrier for installation.
Bottom barriers can limit plant growth.

Sand and pea gravel blankets

Sand blankets are often used in conjunction with bottom fabrics to reface the bottom of a pond. A layer of sand is applied across a fabric or directly on the bottom of the pond completely changing the composition of the existing substrate. Established aquatic plants are smothered while new plants may find it difficult to thrive in this altered environment. This method causes immediate and drastic changes to the pond so it is important to consider the impacts prior to implementation. It is not uncommon for the sand to slide down the bottom slope and contribute to filling in the pond. In limited areas, washed peagravel may be a better alternative because it stays in place better and offers some habitat. Placement of sand blankets in a public waterway requires a permit and is typically restricted to peagravel type material with no underlayment of fabric. No permits are required to lay sand or pea gravel in private ponds.

Drawdown

Drawing down or de-watering your pond is usually used in combination with sediment removal or perhaps shoreline stabilization projects. Following a drawdown, aquatic plants are controlled through drying, compacting or freezing. Winter and summer drawdowns are acceptable for wildlife ponds where fish are not an important component and drawdown is scheduled to minimize impacts to hibernating amphibians. Obviously, complete drawdowns are not compatible with maintaining a viable fishery. Depending on the water depth and water source of your pond, partial drawdowns can be used to manage shallow water vegetation while still maintaining some fish habitat. Aquatic plants can return in abundance once your pond is refilled. This is because the pond sediments often act as a seed reservoir, favoring those aquatic plants with abundant seed reproduction. On the positive side, these bountiful seeds are used as food by all sorts of wildlife including waterfowl and mammals. Drawdowns in private ponds that result in a discharge of water to other waters of the state which includes wetlands, may require DNR approval.

Biological management methods

Little critters

There are a number of biological control agents for aquatic plants, algae and even sediments being researched throughout the world. Research is being conducted in Wisconsin and in other states on the viability of a weevil (Euhrychiopsis lecontei) as a biological control agent for Eurasian water milfoil and on the ability of several species of beetles and weevils to repress purple loosestrife growth. There are also some coordinated efforts to raise and stock beetles for purple loosestrife control across the state. More information can be obtained from your local DNR office. However, the milfoil weevil is probably more suitable to use on large infestations of milfoil in large lakes and, at the present time, would probably be cost prohibitive on smaller ponds ($1 per weevil). Permits from DNR and even from the Department of Agriculture, Trade and Consumer Protection (DATCP) may be required to stock these bugs.

A Milfoil Weevil

Enlarged milfoil weevil

One commercially available biological control method is to stock or augment native bacteria to increase the breakdown of organic sediments. Although this technique may have the potential to reduce organic sediments within a pond, there are contradicting scientific reports about the effectiveness of stocking bacteria in lakes and ponds. Be sure to ask the suppliers of these bacteria for objective documentation about the effectiveness of this method. At the present time, no DNR permits are required for native bacteria augmentation.

Fish stocking

Stocking of fish is also considered a biological management method, although most pond owners stock fish for recreational purposes. Some research has indicated that if lakes are managed for large predator fish, the frequency and abundance of algae can be reduced through manipulation of the food web. Although there is little data available on ponds, in theory, this could work in ponds. Probably the most well known biological management method -- stocking grass carp to control aquatic plants -- has not been permitted in the State of Wisconsin because of the negative impacts to native fisheries and aquatic plants. In the northern tier of states, aeration during winter of shallow ponds will probably be necessary to avoid winter fish kills.

For more information on fish stocking, see the UW-Extension publication [exit DNR] #G3693, "Managing Wisconsin Fish Ponds." A permit is required to stock a pond under Chapter 29.736 of the Wisconsin State Statutes. There is no charge for a fish stocking permit. Applications for this permit are available at your local DNR Service Center.

Private fish hatcheries

Recent legislation passed in September 1997 transferred the regulation of private fish hatchery ponds from the DNR to the DATCP. You can request a Fish Farm Starter Packet from the DATCP [exit DNR]. Although the DATCP now registers fish farms, there are a number of environmental permits that may be applicable to fish farms (see DNR publication #PUB-FH-059, "Environmental Permits for Fish Farms [PDF, 63KB]").

Back to Part I | Forward to Part III

Last revised: Thursday October 31 2013