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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

February 2001

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Measuring a stream's width, depth, flow rate, temperature, pH, dissolved oxygen and nutrient levels. © Mike Miller
Measuring a stream's width, depth, flow rate, temperature, pH, dissolved oxygen and nutrient levels. © Mike Miller

Assessing aquatic health through monitoring

Monitoring helps in the diagnosis.

Mike Miller


The pulse of aquatic health: A result of land and water activities.

Like a doctor making a diagnosis, we can monitor the health of streams and lakes by collecting and analyzing physical, chemical and biological data.

Monitoring documents how environmental changes affect fish and other aquatic organisms. The data also improves our understanding of how human actions affect ecosystem health.

Table of Contents

Monitoring can be targeted to provide information on specific resources and projects, or can be broad to measure statewide trends to maintain quality resources. We monitor some waters by setting up stations that continuously measure water quality and automatically transmit results to computers. In other cases, we select sites and bring in portable equipment to do seasonal, temporary or one-time sampling to answer a specific question.

Historically, aquatic monitoring in Wisconsin focused on commercial and sport fish. We also collected water chemistry data on major industrial rivers. Increasingly, we monitor aquatic ecosystems and evaluate how activities on land affect the waters.

To monitor aquatic health, DNR biologists consider the following:

  • physical characteristics of waterway, size and water temperature, and shoreline and aquatic habitat.
  • watershed land use activities.
  • chemical characteristics of water such as pH, dissolved oxygen and nutrient concentrations
  • the types, numbers, size and health of fish found in lakes or streams
  • the types, and numbers of invertebrates like aquatic insects and mussels found.

Fish species are not equally sensitive to environmental degradation. The ones that are more sensitive make good indicators of healthy waters much like a canary in a coal mine. If these species are found in large numbers, we sense that the lake or stream is in pretty good shape.

Fisheries staff also evaluates if a lake or stream is as productive as it might be. We take steps to help a water body reach that potential and monitor for subsequent changes. As habitat and species change, we modify management practices accordingly.

DNR also monitors fish populations to assess how stocking fish changes natural reproduction rates, determine if changing fish regulations are effective, and note if habitat management activities work.

Measuring what anglers catch in creel surveys helps document angler satisfaction and expectations and the influence of angling pressure on game fish.

We especially enjoy hands-on work with fish. Game fish such as walleye, catfish and trout, as well as nongame fish, are captured with electrofishing equipment or nets. Species, numbers, lengths, weights, ages and other information are recorded; fish are released unharmed.

Aquatic insects and other stream invertebrates also are good indicators of stream health. Like fish, aquatic invertebrates vary in sensitivity to pollution and habitat degradation.

We enlist help to monitor Wisconsin's vast aquatic resources. The Self-Help Lake Monitoring program is a core of 900 volunteers who measure water clarity and water chemistry. Their collective reports alert scientists to potential problems and provide a general picture of the lake's overall health.

Volunteers also note the presence or location of exotic animals and plants by watching for Eurasian water milfoil and zebra mussels.

The DNR also works with institutional partners such as Native American tribes, the U.S. Environmental Protection Agency, U.S. Geological Survey, universities and the State Lab of Hygiene to sample waters and interpret readings. One recent partnership with the University of Wisconsin's Environmental Remote Sensing Center attempted to measure lake water clarity using satellite images.

We believe – and the public expects – that Wisconsin's aquatic resources will be managed with the best scientific information available to ensure that we can enjoy and sustain these resources into the future. Monitoring is a key tool to make that happen.

The pulse of aquatic health: A result of land and water activities.

Clean water in not enough to ensure that lakes and streams are fit for aquatic organisms. Pollution from rural and urban land uses add sediment, nutrients, toxics and pathogens to the water. Phosphorus from manure and commercial fertilizers, may cause excess nutrient concentrations (eutrophication) in lakes and streams and lead to algal blooms.

Sediment, by volume, is the greatest pollutant in Wisconsin's surface waters. Sediment that runs off the land and into the water blankets stream and lake bottom habitat with excess nutrients, making water cloudy reducing the productivity of aquatic ecosystems and blocking sunlight.

Water quantity also changes a lake or stream's health. Flooding can wash vegetation and soil along waterways. Concrete and pavement carry pollutants, increasing runoff and decreasing spring flow to lakes and streams. The water that enters the stream is warmer and lower in oxygen capacity.

Food chains in lakes and streams also factor into an aquatic ecosystem's health. Organic matter such as leaves and other vegetation wash into streams providing food for aquatic insects, which in turn, are food for other aquatic organisms that live there.

Mike Miller is a DNR monitoring specialist.