Water Quality Management
Overview
Managing Water Quality
Our lake water quality monitoring program gathers samples on District lakes throughout the early spring, summer, and fall. This is considered the growing season when the lake is the most productive.
We measure and monitor lake water clarity, conductivity, pH, temperature, and dissolved oxygen. We monitor aquatic invasive species (AIS), like Eurasian watermilfoil and zebra mussels.
In addition, we collect water samples that are analyzed for chloride, phosphorus and chlorophyll-a. The District has established goals for annual average Secchi reading, chlorophyll-a and phosphorus in our managed lakes.
Monitoring
Managed lakes are monitored throughout the year. Lakes are monitored for known and unknown AIS, chlorophyll-a, phosphorus, chloride, water clarity, pH, temperature, nutrients, and dissolved oxygen.
Chlorophyll-a
Chlorophyll-a measures the amount of algae and cyanobacteria in a waterbody. Algae and cyanobacteria are natural parts of a freshwater ecosystem. However, too much can create bad odors, aesthetic issues, and decreased levels of dissolved oxygen. Some cyanobacteria can produce toxins which are harmful to people and animals. Nutrients from fertilizers, septic systems, and stormwater runoff contribute to high chlorophyll-a levels.
Phosphorus
Phosphorus is a chemical element that is essential for living cells. When phosphorus is excessive, it can cause eutrophication and harmful algal growth. Excess phosphorus typically comes from things like:
- Lawn fertilizers
- Agricultural fertilizers
- Animal by-products like manure
- Wastewater treatment facilities
What is eutrophication?
When water becomes overloaded with nutrients, it can become eutrophic or experience eutrophication. There is an unnatural imbalance of nutrients in the water, such as nitrogen and phosphorus. This results in excessive algae growth, and the beginning of a chain reaction in the ecosystem. The excess algae blocks out sunlight to underwater plants. This reduces aquatic habitat, and lowers oxygen levels. When the algae eventually dies off and decompose, they consume even more oxygen in the water. This compounding effect creates an environment with oxygen levels too low to support most aquatic life. Eventually, the waterbody can become anoxic, and the dissolved oxygen in the water is 0. When a lake becomes anoxic, it is considered dead and uninhabitable.
Chloride
Chloride is a chemical commonly used to melt ice during the winter. It makes its way into the water through stormwater runoff. Chloride is toxic to fish, aquatic insects, and amphibians. It also harms plants, soil, pets, infrastructure, and can contaminate drinking water.
Water Clarity or Turbidity
Water clarity is an indicator of water quality. It is a misconception that all lakes and streams should be completely crystal clear. In fact, a healthy lake will often have some level of sedimentation and many aquatic plants present. Water clarity can be referred to as turbidity.
pH
pH is the measure of how acidic or basic water is. The pH scale ranges from acidic at 0 to alkaline at 14, with 7 being neutral. In lakes and streams, the pH level influences nutrient levels, fish reproduction, and habitat suitability for macroinvertebrates and amphibians.
Temperature
Water temperature influences many of the physical, biological, chemical, and ecosystem processes in lakes and streams. Increased water temperature can decrease dissolved oxygen, make it easier for metals and other toxins to dissolve, create algal blooms, and create unsuitable habitat conditions for fish species like cold water trout.
Nutrients
Nutrients in water quality testing most commonly refers to phosphorus, nitrogen, and E. Coli. These nutrients most commonly enter lakes and streams through runoff containing yard and agricultural fertilizers, pet and animal waste, and leaves and grass clippings. Nutrients support plant grow, but excess nutrients can trigger algal blooms.
Dissolved Oxygen
Dissolved oxygen (DO) is the amount of oxygen in the water and is essential for fish and other aquatic life. When algae dies and begins to decay, the process consumes available oxygen. When there an excess of decaying matter, the process can consume so much oxygen, and cause fish and other aquatic life to die, often referred to as fish kills.
Management
When an invasive species is detected, the District takes action to manage the population. It is impossible to know when exactly an aquatic invasive species enters a lake. It is common for invasive species to be introduced through recreational use of a lake. That is why it is important to always remember to Clean, Drain, Dry before entering and exiting any body of water. Shallow and productive lakes like those in the watershed are ideal habitats for aquatic invasive species to thrive and outcompete native species
AIS in the watershed
Aquatic Invasive Species, or AIS, refers to species of aquatic plants, fish, invertebrates and macroinvertebrates, that are not native to a body of water. Like invasive species on land, aquatic invasive species lack natural predators to control their population, may reproduce or spread quickly, and outcompete with native species for food, light, and habitat, leading to biodiversity loss.
Eurasian watermilfoil (Myriophyllum spicatum) and Curly-leaf pondweed (Potamogeton crispus) are both found in the watershed. While these species are now found throughout the twin cities metro, it is still important to manage their populations. Managed waterbodies are assessed for treatment during twice annual monitoring surveys and treatments are prescribed if necessary.
Goldfish
Goldfish (Carassius auratus) are an aquatic invasive species (AIS) that hurts water quality. It is critical that unwanted aquarium fish and plants are never dumped into lakes, creeks, or ponds.
Goldfish are a species of carp. Just like carp, goldfish swim along the bottom of water bodies, stirring up sediment and releasing nutrients into the water column. This behavior creates cloudy water, and the nutrients released can cause algae blooms. Goldfish can out compete with native fish species because of their rapid growth, high reproduction rates, and competition for food and space.
Why are some lakes treated?
Invasive species like Eurasian watermilfoil and Curly-leaf pondweed are a nuisance. They make recreation like fishing, canoeing, or kayaking quite difficult. Additionally, Curly-leaf pondweed grows in the winter and spring before other native species. After Curly-leaf pondweed dies, it releases nutrients into the water that drive ongoing algae blooms.
How are lakes treated?
When an herbicide treatment is deemed necessary, a permit is obtained from the MNDNR. In-lake herbicide treatments have been around for a long time and studied extensively. Research shows that they do not harm fish, mammals, or aquatic insects, and are safe for humans and pets. When a treatment occurs, signage is clearly posted to notify lake users of ongoing treatments and recommended uses.
How should I interact with treated lakes?
Depending on the treatment type, there are time limited restricted activities following treatment. After a lake is treated, a notice will be posted on site with specific restrictions based on the time of application.
Restrictions following treatment with Sonar A.S. (Fluridone):
- There is no restriction swimming
- There is no restriction on human consumption or ingestion
- There is no restriction on domestic use, such as laundry or cleaning
- There is no restriction on human consumption of fish
- Treated water should not be used for irrigation of food crops for 14 days after application
- Treated water should not be used for irrigation of landscape plants or turf for 14 days after application
- There is no restriction on livestock consumption
Check out this video on in-lake treatments on Colby Lake to learn more about how SWWD manages aquatic invasive species
Abby Tekiela
Staff Contact
Questions? Reach out to Abby Tekiela, Water Resources Program Manager, at Abby.Tekiela@swwdmn.gov or call 651.728.6827.