Silver Lake IA 01-MAQ-17

Assessment Comments

Monitoring conducted in 1990 by ISU as part of Clean Lakes Classification study (1994).

Basis for Assessment

Lake assessed as PS for the 1992 report for the following reasons:  (1) DNR field staff assessed the lake as PS due to impacts from nutrient and sediment, (2) results of monitoring in 1990 show that mean levels of total-P and chl-a are worse than overall means of 116 SPOLs sampled in 1990 and 1992 + 1 SD, thus suggesting a nutrient enrichment problem, and (3) lake has winterkill frequency estimated at nearly 15%.   Although designated for swimmable uses, lake does not have a swimming beach, and Bachmann et al.  report swimming use as zero; thus swimmable use not assessed.   Lake has a very low sedimentation rate (1.0 cm/yr) and a relatively long life expectancy for an SPO impoundment in Iowa; thus, ag NPSP is probably much less of an impairment than is lack of sufficient depth to allow thermal stratification (mean depth = 6').