Assessment Comments
Assessment is based on results of (1) ISU lake survey in 2000-01, (2) surveys by IDNR Fisheries Bureau, and (3) ISU report on lake phytoplankton communities.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation uses) are assessed (monitored) as "not supported." The Class B(LW) aquatic life uses are assessed (evaluated) as "partially supported." Fish consumption remain "not assessed." Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted in 2000 and 2001 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, and (3) information on phytoplankton communities at Iowa lakes in 2000 from Downing et al. (2002). EXPLANATION: Results of monitoring conducted by ISU in 2000 and 2001 as part of the statewide survey of Iowa lakes suggest that the Class A (primary contact) uses are "not supported." Using the median values from this survey in 2000 and 2001 (approximately six samples), Carlsons's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 88, 75, and 83, respectively, for Crystal Lake. According to Carlson (1977), these index values place this lake in the upper range of hyper-eutrophic lakes and suggest excessive phosphorus loading to the water column, excessive, but somewhat less that expected, production of suspended algae, and (3) very poor water transparency. In addition, levels of inorganic suspended solids at Crystal Lake are relatively high. The median level of inorganic suspended solids in the 130 lakes sampled for the ISU lake survey in 2000 and 2001 was 5.27 mg/l. The median level of inorganic suspended solids at Crystal Lake (17.9 mg/l) was the fourteenth highest of the 130 lakes, thus strongly suggesting that non-algal turbidity limits the production of algae. These conditions indicate impairments to the Class A (primary contact) uses through presence of aesthetically objectionable blooms of algae and presence of nuisance algal species (i.e., bluegreen algae). Data from Downing et al. (2002) suggest that bluegreen algae (Cyanophyta), can, at times (especially late summer), dominate the summertime phytoplankton community of Crystal Lake). Sampling at Crystal Lake in summer 2000 showed that bluegreen algae comprised approximately 50% of the phytoplankton community in the early Julyl sample, less than 5% in the late July sample, and approximately 90% in the early September sample. Based on median values from ISU sampling in 2000 and 2001, the ratio of total nitrogen to total phosphorus for this lake is 8. The hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses are "partially supported" due to excessive nutrient loading to the water column, nuisance blooms of algae, and re-suspension of sediment. Fish consumption remain "not assessed" due to the lack of recent fish contaminant monitoring at this lake.
