Since 2008, Diamond Lake has been part of an annual monitoring program called WHEP (Wetland Health Evaluation Program), which monitors wetlands throughout Hennepin County. The monitoring follows a rigorous protocol to give results that are comparable year-to-year. Both shoreline plants and water macroinvertebrates (such as dragonflies, snails, water boatman, and leeches) are sampled, the plant varieties are catalogued and the macroinvertebrates are categorized by species and number.
Diamond Lake appears as a lake on maps but its shallow depth and vegetation place it in the DNR’s classification as a Type 4 wetland. At a maximum of 5.8 feet and average depth of 3.2 feet, Diamond Lake biologically functions like a wetland and its health is more accurately measured by using wetland metrics than lake metrics.
The macroinvertebrates in particular are biomarkers of the water body’s health. Some are more tolerant of poor water quality and others are found primarily in water of higher quality. Over the past nine years of monitoring, two general observations can be made:
- The shoreline vegetation has shown a lack of diversity with increases in the quantity of invasive plants. This is at least partially due to the presence of muskrats breaking up cattail beds and allowing new plant species to become established.
- The macroinvertebrates have shown some increase in diversity with more of the ‘bugs’ being those that are found in higher quality water bodies.
The trend in macroinvertebrate findings is encouraging. Diamond Lake will always face water quality challenges because it is a small 55-acre body of water dependent on stormwater runoff from over 900 acres of urban development, including highways, streets, driveways, alleys and lawns.
Mature trees, rain gardens, and pervious paver surfaces can all help to improve the water quality of Diamond Lake by controlling the sediment and nutrients flowing into the lake.