Contact: Cori Rude-Young, 651-757-2680
St. Paul, Minn. — A public comment period will begin Feb. 4 and continue through March 6, 2013, on a revised water quality standard proposed for Lake Hiawatha in Minneapolis. The proposed target is specific to the lake and addresses nutrient levels.
Lake Hiawatha is located in the lower end of the Minnehaha Creek watershed in Minneapolis. It is popular for swimming and fishing. However, because of phosphorus entering the lake, Lake Hiawatha suffers some years from algal blooms and diminished clarity, which limits recreational opportunities on the lake.
The Minnesota Pollution Control Agency (MPCA), along with the Minnehaha Creek Watershed District and the U.S. Environmental Protection Agency, is conducting a study of the lake. This study, called a Total Maximum Daily Load, includes first setting water quality standards specific to Lake Hiawatha.
The need for a site-specific water quality target for Lake Hiawatha arises because the lake receives drainage from a very large area — more than 170 square miles — via Minnehaha Creek. This means that water resides in the lake for only a short time before flowing back into the creek. This is actually advantageous in terms of water quality because a short residence time limits the amount of algae that can grow. This means that it takes a greater concentration of phosphorus to produce a given amount of algae, as compared to more typical residence time conditions.
Lakes in Minnesota are subject to a three-part water quality standard: total phosphorus concentration, chlorophyll-a (the main pigment in algae) concentration and Secchi disk depth (a measure of water clarity). These apply as a June-through-September average. The MPCA proposes changing only the total phosphorus portion of the standard for Lake Hiawatha, specifically from 40 to 50 micrograms per liter.
During the last 12 years, the lake has averaged slightly more than 70 micrograms per liter. It is expected that reducing phosphorus levels to 50 micrograms per liter will result in the lake’s also meeting existing standards for chlorophyll-a and Secchi disk depth. If these standards are achieved, algal blooms should be minimal, and the lake will have more desirable water clarity, so it is suitable for fishing, swimming and other recreation.
Details of the proposed site-specific standard can be found on the MPCA’s Minnehaha Creek Bacteria and Lake Hiawatha Excess Nutrients webpage.
To receive more information or submit comments on this proposed site-specific standard for Lake Hiawatha, contact Chris Zadak, MPCA, 520 Lafayette Rd. N., Saint Paul, MN 55155; phone 651-757-2837 or 800-657-3864; or email chris.zadak@state.mn.us.
