Clear Lake IA 02-WIN-841

Assessment Comments

Assessment is based on results of water quality monitoring, RAFT tissue sampling, and surveys of the DNR Fisheries Bureau.

Basis for Assessment

Assessed support of the Class A primary contact recreation uses as FST due to excessive growth of phytoplankton resulting from excess nutrients (primarily phosphorus) in the lake.   Hypothesized sources of excess nutrients include runoff from urban areas, agricultural runoff, naturally high soil fertility, effects of carp and other bottom bottom feeding fish, and nutrient export from nearby wetlands.  During the reporting period, blooms of algae have been recognized as detracting from the aesthetic appeal of the lake for swimming, water skiing, and other Class A-type uses.   A recent WQ evaluation by Wisconsin limnologist Paul Garrison suggests that, in terms of nutrient levels and levels of algae, lake water quality has been declining since the 1940s with even more rapid decline over the last five years.   Several efforts are underway to address this problem, including the Clear Lake Enhancement and Restoration Project (CLEAR) and year-long WQ study proposed by limnologists at Iowa State University to identify specific sources of nutrients and recommend actions to correct WQ problems.   Class B(LW) aquatic life uses were assessed as FS:  the DNR Fisheries Bureau reports that Clear Lake has supported above average fish populations over the last few year.   The March/April 1998 Iowa Conservationist reports that Clear Lake provides good to excellent angling opportunities for walleye, muskellunge, and channel catfish.   The Class C drinking water uses designated for the lake were not assessed: no data or other information are available for developing an assessment of these uses.   Continue to assess fish consumption uses as FS:  levels of all contams in the sample of channel catfish fillet collected for the 1993 RAFT were < 1/2 FDA levels.