TMDL & Water Quality Assessment Section - 2004
The Federal Clean Water Act requires the Iowa Department of Natural Resources (IDNR) to develop a total maximum daily load (TMDL) for waters that have been identified on the state’s 303(d) list as impaired by a pollutant. Silver Lake has been identified as impaired by algae and turbidity. The purpose of these TMDLs for
Silver Lake is to calculate the maximum allowable nutrient loading for the lake associated with algae and turbidity levels that will meet water quality standards.
This document (link above) consists of TMDLs for algae and turbidity designed to provide Silver Lake water quality that fully supports its designated uses. Phosphorus, which is related through the Trophic State Index (TSI) to chlorophyll and Secchi depth, is targeted to address the algae and turbidity impairments.
|You've likely heard of Iowa's many "impaired" waters. But what makes a water impaired, and more importantly, what can we do to take streams and lakes off the list? |
Each lake and stretch of stream or river in Iowa is designated for a specific use, like for contact recreation such as swimming or fishing; for drinking water; or for maintaining a healthy population of fish and other aquatic life. If the water quality in the stream or lake does not allow it to meet its designated use, it does not meet Iowa's water quality standards and is considered "impaired."
The waterbody is then placed on the "303(d)" list, commonly known as the "impaired waters list." This is named after section 303(d) of the federal Clean Water Act and means that the stream or lake needs a water quality improvement plan written.
Once on the 303(d) list, a water quality improvement plan is written. The plan outlines the water quality problems, identifies the needed reductions in pollutants and offers possible solutions. Waters that have a water quality improvement plan written for them move off the 303(d) list, or impaired waters list.
Even though it's off the 303(d) list, the waterbody is still considered impaired until water quality improves. Local groups need to take action and work with the DNR to improve their stream or lake.
Local action can lead to improved water quality, which can help the stream or lake meet state water quality standards again. When the waterbody meets those standards, it may be able to come off the impaired waters list.
Final 2008 Impaired Waters in Iowa: 439