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Brickyard clayhole lake in Chaska

Map of the three clayhole lakes, with watershed boundaries.

Click on pic above for clayhole lake data (size of lakes & watershed, depth, etc.).

Metro area lakes are graded according to criteria developed by the Met Council: total phosphorus, algae growth, and clarity. According to these criteria, the three Chaska clayhole lakes rank A & A-. Click above for a chart of ratings.

An erosion "hot spot" on the banks of Firemen's Lake.

water quality of chaska's clayhole lakes passes muster

In November, Watershed District consultants Bonestroo Rosene Anderlik & Associates published a surprisingly glowing report on the three downtown Chaska clayhole lakes — Firemen’s, Brickyard, and Courthouse. Brickyard and Courthouse, on the east side of trunk Highway 41, are within the Watershed District, and Firemen’s, to the west, drains into it. In all three lakes, the overall water quality is high, and esthetic and recreational values continue strong.

Report author Rich Brasch thinks that overall the “lakes are in very good shape. I expected to see signs of moderately severe degradation,” he says, based on experience with other metro lakes, “but from a water quality standpoint the lakes are probably in the upper ten percent of all lakes in the metro area.”

What does this happy condition owe to?

Why the water quality's so good

Brasch cites several factors:

• The area is not developed as much as other nearby cities, and thus lacks big pollution loads.

• Each lake has a small watershed-to-lake ratio.

• Both Firemen’s and Brickyard lakes have storm sewer diversions, installed by the city in 2001, which keep out runoff with the highest pollutant loads, like phosphorus, from farm fields and yards.

All three lakes are rated “mesotrophic” by the Met Council and support full recreational uses — swimming and fishing, including body contact. (See our 2002 article on the economic and ecological history of the lakes.)

Click here for an up-to-date report card on the clayhole lakes' water quality.

What can be done to safeguard the water

But the high quality of present water doesn’t mean there are no threats to the lakes.

In fact, the city of Chaska realizes what a valuable resource the lakes are and how, once lost, water quality is almost impossible to restore. In fact, as the Bonestroo report suggests, even the perception of lost water quality might make people wary about using the lakes for recreational purposes. 

Thus, three years ago the city built diversion sewer systems around Firemen’s and Brickyard lakes to keep out excess runoff — and the phosphorus loads that could lead to unsightly algae blooms.

Thus, the city is planning to develop stormwater treatment ponds around these two lakes as housing develops in the future and not to allow any development around Courthouse Lake .

Thus, it is taking under advisement the Bonestroo firm’s water management recommendations, including:

• Education. Through a kiosk or sign by each lake, visitors will learn about the exceptional condition of the lakes and the measures needed to keep them that way.

• Trash. Trash would be cleaned up from the lakes and shores and, with the aid of the education measures, people might be persuaded not to “let their trash get away from them.”

• Sediment ponds. Chaska and the District should monitor current and future water detention ponds and remove excess sediment, from runoff, if the ponds become less efficient in removing it.

• Courthouse Lake . Elevated phosphorus levels are detectable in the deeper areas of this lake, a consequence of past inundations by the Minnesota River and the lake’s small surface area (10 acres) that prevents full water mixing and aeration. The city of Chaska could install aeration equipment, but that risks mixing poor-quality deep water with the cleaner surface water. Bonestroo has instead recommended adding the chemical alum to “inactivte the high nutrient concentrations in the deeper water,” says Brasch, “and sediment them out, improving water quality.”

• Buffer zones. With the cooperation of riparian landowners, private and public, the City can plan deep-rooted native vegetation and wildflowers. These flora would create a long buffer strip that would filter overland runoff away from more maintained areas, stabilize the shore, and perhaps provide fish and wildlife habitat.

• Weeds. The purple loosestrife evident around Courthouse Lake could be eradicated through pulling and/or chemicals.