This map shows sites that the City of Ames, Story County, and Prairie Rivers of Iowa monitored for E. coli bacteria from 2020-2024.
The map is color coded to show which sites meet primary and secondary recreation standards. Which standard is relevant to you depends on water levels, whether you have small children, and whether you plan on getting submerged in the water. For waters that are not a downstream of a regulated facility, the designated uses may not have been assessed.
E. coli bacteria criteria for recreational waters apply from March 15-November 15, when the water is warm enough that recreational use is possible. A minimum of seven samples are needed in a season to apply the standards. The standard has two parts:
1) A geometric mean for the season should not exceed 126 colonies/100mL (primary contact recreation) or 630 colonies/100 mL (secondary contact recreation).
2) No single sample should exceed 235 colonies/100 mL (primary contact) or 2,880 colonies/100mL (secondary contact). If more than 9 samples are collected, no more than 10% of samples should exceed this threshold.
The color coding on the maps is based on the geometric mean. Use the radio buttons to view different seasons. Click on a point to get additional information, including whether the single-sample maximum was violated. Streams that normally meet the standards may still have high E. coli levels immediately after heavy rains.
Green = Meets primary contact recreation standard (<126 colonies/100mL)
Yellow = Exceeds primary contact standard but meets secondary contact recreation standard (126-630)
Red = Exceeds secondary contact recreation standard (> 630)