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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Sticky marl is ground up and pumped through pipes suspended on floating pontoons. © Peter M. Segerson
Sticky marl is ground up and pumped through pipes suspended on floating pontoons.

© Peter M. Segerson

June 2007

Spring cleaning a fishery

Rehabbing spring ponds pumps up Northwoods trout streams.

Peter M. Segerson

There is a saying among limnologists that all lakes are born to die. It's not that scientists are gloomy, brooding people. After all, they get to spend a lot of their time outdoors looking at lakes. It's just that if you take the long view of what happens to waters over hundreds or thousands of years, as soon as lakes are carved out of the landscape they start aging, just like people. In lakes, this natural process is called ecological succession and the lakes start filling in again to become pockets of bog, swamp or some other natural community.

When the Wisconsin glaciers finished their geologic shoving match more than 10,000 years ago, they pushed ahead and left behind large glacial lakes, river dells, rubble and cobble moraines, boulders, outwash plains of sand and gravel, and countless kettle holes. In northeastern Wisconsin, some of those kettles remain as spring lakes and ponds; small potholes where groundwater wells up to the surface. In northern Wisconsin soils, conifers surround these fertile, clear ponds and the alkaline waters take on a unique hue and character.

In the northern clime, many trout streams begin as the outlet of a warmwater lake or as bog and swamp drainage. These waters draining a larger area combine with the cold waters flowing from spring ponds to form headwater streams where trout will thrive.

Langlade County, where I worked, is true headwaters country. At least 200 spring ponds (the most of any Wisconsin county) feed many streams and rivers including the Wolf, Oconto, Prairie, Plover and Eau Claire rivers.

Back in the 1930s and '40s, trout anglers and the Wisconsin Conservation Department recognized that these spring ponds formed the lifeblood of fine fishing and began protecting and acquiring these small ponds. Hundreds of parcels were purchased throughout the state to protect springs and coldwater streams. Some of those spring ponds saw considerable disturbance from their natural state. They were used to water livestock, bottle soda pop and grow trout raised at private fish hatcheries. Various structures like beaver dams, manmade impoundments and poorly designed road culverts also disrupted water flow. Purchasing the ponds and rehabilitating them was an important step to sustain a flow of clear, cold water to trout streams.

The Conservation Department and private landowners experimented with assorted dredging equipment, pumps and draglines to rehabilitate spring ponds in the 1950s. Most attempts were not successful. In 1965 the department purchased two amphibious cutter head hydraulic dredges from National Dredge in Beloit. It is testament to the military engineers who crafted these dredges from American-made steel and the mechanical ingenuity of several DNR employees that more than 60 years later, one of the machines is still operating on a daily basis.

The dredge was built from a 1943 military tracked landing vehicle, so it has a rock steady base with a Detroit Diesel power plant. During the seventies and eighties, ingenious fisheries technicians Marvin Zaddack, Irvin Aird and Lawrence Pomasl added a swinging ladder, an all-weather cab and pontoon flotation to the dredge. In 1992, Jeff Reissmann led a major overhaul of the Antigo dredge at the DNR's Tomahawk Equipment Facility. Numerous parts were fabricated and the Spooner dredge was cannibalized to make one unit out of two.

The whole device looks a bit like a little office with windows sitting on top of an amphibious tank with a giant arm at the front end. At the end of the arm, a rotating cutting tool looks a bit diabolical, like it was invented by some deranged villain to drill through buildings, thick steel-walled safes or concrete walls to reach some cloistered treasure. In fact, the bit has to dig through material that at times seems nearly as tough and thick.

Spring pond rehabilitation has two major goals: to clean gravel sites to restore the flow of upwelling groundwater, and to remove accumulated silt, marl and organic debris. The upwelling groundwater is vital for brook trout reproduction. Removing marl and peat layers deepens the ponds providing living space for trout and aquatic plants, insects and other animals.

Over decades and centuries, the bottom of these clogged up ponds built up a thick sediment layer of decaying leaves, boggy plants and muds. This "marl" is a thick, sticky mass of clay, bits of shell and calcium carbonate that is light in color. When wet, marl has the thick consistency of slippery modeling clay. The whirling cutting bit loosens up the muddy marl that is sucked through a pipe in the middle of the bit using a powerful sand and gravel pump – powerful enough to carry fist-sized rocks and mud uphill more than a 100-foot grade through a pipeline that can extend up to three-quarters of a mile. The sticky slurry is pumped over the water in a floating pipeline that drains into a nearby bermed storage area on land.

Hydraulic dredges are modified World War II tracked amphibious landing vehicles. © Peter M. Segerson
Hydraulic dredges are modified World War II tracked amphibious landing vehicles.

© Peter M. Segerson

Water settles out of the slurry quickly. What's left is a rich material that can be used for fertilizer on lime-deficient soils or a soil conditioner for sandy soils. The lime in marl cements sand grains together and also has the opposite effect of loosening up clay soils. The calcium carbonate in marl is also a component of Portland cement, so clean marl can be sold. Peat layers in the dredged mix come out of the pipe as a black slurry. As these dry out, they form a rich mix that can be used as a soil conditioner or potting soil. More often than not the spoil piles from such dredging operations are left in a depression and after a few growing seasons the organic soils can be planted and managed to form wildlife cover or food plots.

Before dredging begins, a short access road of cut timber (called a corduroy log mat) is laid down to provide a path to get the heavy dredge into and out of the water. The launch site is restored as part of the project after the dredge is removed.

Dredging operations start at the upper end of a spring pond and work downstream toward the outlet. Before any dredging begins, sediment mats and floating oil boom equipment are placed at the outlet to trap sediments stirred up during dredging and prevent downstream problems.

The dredging crews suck out the organic, muddy sediments until they reach underlying layers of sand, gravel and rubble. These clean, hard layers can be colonized by plants, invertebrate insects and small fish to start building a full fish community. Trout also return as the ponds, redds and beds recover. The dredging crew often fell some trees along the shoreline to provide some secure overhead cover for trout. Reptiles like painted turtles, wood turtles and northern water snakes as well as dragonflies and other insects, find refuge and resting areas on these dropped trees.

Anglers come back to these recovered waters seeking trout. Brook trout are Wisconsin's only native stream trout and their Latin name, Salvelinus fontinalis, translates as "char of headwater ponds." Studies of rehabilitated spring ponds have found three to five times more biomass (lbs/acre) of trout after ponds are dredged and the coldwater community starts to naturally restore itself.

A dedicated following of anglers has learned how to fish these ponds. Shore fishing here is difficult and soggy due to boggy, cedar-lined banks. Wade fishing can be downright dangerous due to deep, sticky marl and silty areas, so local anglers became accustomed to fishing from canoes and small pram type boats. Float tubes have recently become the watercraft of choice as anglers can easily carry them into remote access points on these ponds. Fly fishers find success using small streamers, wet and dry flies with specialized local patterns. Live bait dunkers and artificial lure pitchers also fish these spring ponds effectively.

These waters open for fishing during the general trout season from the first Saturday in May through the last day of September. Fishing regulations vary and are tailored to the size of the pond, potential trout growth and the particular trout species. Nearly all the ponds hold brook trout, some also have brown trout, and a few have rainbows. There is little stocking of spring ponds since nearly all support excellent natural reproduction of trout. Come and try your luck and enjoy the scenery in these cozy settings surrounded by conifers and restored, clean, cold waters.

Peter M. Segerson now oversees fisheries operations for the Department of Natural Resources in the Black River Falls area. For further information on the spring ponds in the Antigo area, contact fisheries biologist Dave Seibel or pond habitat crew leader Jeff Reissmann at the DNR Service Center, 223 E. Steinfest Road in Antigo, (715) 627-4317. Call ahead for office hours.