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Water Quality

The RPBCWD staff is out on the water year-round monitoring the quality of our lakes and creeks. Read on to learn about some of the things they look at to determine the health of our waters, or click the banner below to view the health of the individual lakes in our district:

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A majority of the phosphorus in lakes comes from agricultural or urban run-off. Phosphorus is a major component of the fertilizers used to grow crops, and is found naturally in grass clippings, leaves, and other organic matter that wash into our storm drains or directly into our lakes. Without BMPs in place to intercept and filter the nutrients out of the water, the phosphorus makes its way into our lakes and streams where it negatively impacts our water quality.


Chlorophyll-a is the main pigment in algae, and is useful for measuring the concentration of algae present in a lake. Measurements are taken from water samples collected by a Van Dorn, an open-ended tube that allows you to capture water samples from a specific depth by lowering it and triggering the closure of the end plugs. Chlorophyll-a levels are a good indicator of the trophic level of a waterbody. 


Increasing chloride levels in water bodies are becoming of greater concern within the state of Minnesota. It takes only one teaspoon of road salt to permanently pollute five gallons of water, as chlorides do not break down over time. At high concentrations, chloride can be harmful to fish, aquatic plants, and other aquatic organisms.

Dissolved Oxygen

Dissolved oxygen (DO) is a measure of the amount of oxygen present in the water. As all aquatic life needs oxygen to survive, monitoring a waterbody's dissolved oxygen levels is a great way to evaluate the health of a lake through it's ability to support aquatic life. 

Secchi Disk

Secchi disks are used to measure water clarity. It is calculated by lowering the disk into the water and marking the depth at which the disk disappears from view, reeling it back and marking the depth it reappears, and averaging the 2 numbers. A lake with good water clarity means sunlight can travel further down the water column, where it will be made available to aquatic life. 

Zebra Mussel Veliger Sampling 

RPBCWD staff conducts veliger tows each spring, sending a net with a collection cup attached to the end down to the lake bed. Once back at the surface, the water in the net will drain out through the collection cup, leaving any veligers trapped behind. Zebra Mussel veligers (larvae) were found in Lotus Lake in 2019 by Carver County, but have not been found in any veliger tows conducted by RPBCWD to date. 


eDNA, or Environmental DNA, is the DNA of an organism detected in it’s environment, such as water or soil, rather than from the organism itself. eDNA is a useful tool for detecting the presence of zebra mussels in an aquatic ecosystem early before they become too plentiful. eDNA was used to confirm the presence of zebra mussels in Lake Lotus following the discovery of zebra mussel veligers.

Dive Deeper

Want to learn more? Read the full 2020 Water Resources Report.
For specific water quality questions or concerns, contact our Water Resources Coordinator Josh Maxwell at