Iowa DNR

Water Quality Assessments

Impaired Waters List

ADBNet Documentation

Impaired Waters

You’ve likely heard of Iowa’s many “impaired” waters. As the Iowa Department of Natural Resources prepares the latest version of the state’s impaired waters list, it’s important to understand what makes a water impaired, and more importantly, what we can all do to take streams and lakes off the list.

The list of impaired waters is only as inclusive as the various water quality (WQ) monitoring networks in Iowa. In general, when the amount of monitoring data increases, the number of waters on the Impaired Waters list also increases. The identification of impairments is also strongly tied to the state’s water quality standards; therefore, because Iowa does not yet have numeric WQ criteria for nutrients or sediment/siltation, identification of such impairments is relatively rare. Additionally, because Iowa’s WQ Standards also lack criteria for turbidity, any lake or wetland impairments attributed to algae (chlorophyll) or non-algal turbidity are based on violations of the state’s narrative standards protecting against “aesthetically objectionable conditions''. Eventual adoption of numeric criteria for nutrients, chlorophyll, and/or turbidity will likely result in a substantial increase in the number of segments on Iowa’s future lists of impaired waters.

Segments are impaired when data shows that the water quality does not meet the standards of the designated use. A segment may be impaired when water monitoring data may show high levels of pollutants, like nutrients or chemicals, or whenbiological monitoringfinds that fish and other aquatic life populations aren’t as diverse or numerous as they should be. Recreational uses can be impaired when there are high levels of indicator bacteria (E.Coli) or algal toxins such as cyanotoxins and microcystin.

Biological impairments are difficult to trace to a specific cause. Likely causes that degrade stream habitats include siltation, which can reduce spawning success or insect hatches, and low dissolved oxygen. Excess nutrients such as nitrogen or phosphorus can cause algal blooms. These algal blooms, aside from being aesthetically objectionable, can also produce toxins of their own, and have can have detrimental impacts on aquatic life when they decay, which causes dissolved oxygen levels to drop.

As water quality improves, fish and other aquatic life populations should grow and diversify, resulting in healthier biological communities over time.

What does “impaired” really mean? Is the water unsafe?
Much confusion exists regarding the meaning of “impairment” as used for Clean Water Act Section 303(d) listing. In terms of water quality condition, “impairment” is not a “one size fits all” concept and the degree of water quality impairment ranges from slight to severe.

Simply put, a waterbody is impaired when its water quality does not fully support that waterbody’s designated uses for human contact, aquatic life, fish consumption or drinking water. Some of these impairments, like high nitrate levels in the Raccoon and Cedar rivers, could pose a risk to Iowans’ drinking water if not treated for nitrate removal or mixed with other sources of drinking water to lower nitrate levels. The decline in freshwater mussels in many Iowa streams also indicates a severe water quality problem. However, most impaired waterbodies in Iowa are generally not grossly polluted.

Severe water quality problems, although rare, do continue to occur in Iowa. Most of the impairments on Iowa’s draft list of impaired waters, however, do not indicate severely or grossly polluted conditions. Often, the difference between assessing a waterbody as “impaired” versus “fully supported” can come down to contaminant levels in only one of 36 monthly samples or the absence of a few key aquatic species in a stream. Iowa’s water quality standards and numeric water quality criteria—which are the basis for identifying impairments—are designed to be protective of the beneficial uses designated for Iowa’s streams, rivers, and lakes. These criteria are set to warn of potential water quality problems well before anything approaching “grossly polluted conditions” occurs. Many waters assessed as “impaired” for aquatic life uses often continue to support a moderately healthy and diverse aquatic community. Also, the designated recreational uses of many Iowa waters—especially rivers and streams—are impaired by high levels of indicator bacteria, but reports of waterborne illness related to these high levels of bacteria have been extremely rare in Iowa over the last 40 years.

Why does the number of impaired waters in Iowa continue to increase?
A state’s Section 303(d) list of impaired waters is, in part, an accumulation of impairments identified in past listing cycles. Once added to a state list, the impairment is likely to remain on the list. In general, impairments are identified faster than impairments are removed through the TMDL process or due to water quality improvement. Thus, the number of impaired waters on state lists tends to increase over time. Also, as more state waters are monitored over time, the number of impairments also continue to increase.While states can easily add new impairments, the U.S. EPA carefully scrutinizes any state proposal to remove (delist) impairments from a Section 303(d) list and sometimes rejects state recommendations for delisting. In addition, a large proportion of impairments (bacteria and biological impairments) are related to non-point sources of pollution. Unless a state has authority and the means to reduce levels of non-point source pollution, the NPS-related impairments will likely continue to reside on the state’s list of impaired waters.

Do waters ever come off the impaired list?
According to U.S. EPA regulations, impairments can only be removed from a state list for specific reasons, including: (1) more recent data showing that the impairment no longer exists, (2) discovery of an error in the data or rationale for the original listing and (3) preparation and approval of a total maximum daily load (TMDL) that identifies sources of pollutant loadings and reductions in loadings necessary to fully attain applicable water quality standards. A primary mechanism for removing waters from Iowa’s list of impaired waters has been preparation and U.S. EPA approval of TMDLs.

Most segments move off the 303(d) list because water quality improvement plans are written or new data is available. However, relatively few waters came off the list because water quality improved enough to meet water quality standards.

Water quality issues in Iowa did not happen overnight, so improving the waters requires a long-term approach. Projects across the state have seen improvements in water quality. At the Iowa Great Lakes, a collaborative effort – including a local golf course – created a 350-acre wetland and prairie complex. Before the project, 480 tons of sediment washed into West Okoboji Lake with every 2-inch rainfall. Now, it's estimated that the work will reduce sediment reaching the lake from this area by 92 percent, reduce phosphorus by 90 percent and nitrate/nitrogen by 72 percent. The work also helps reduce flooding and creates important wildlife habitat.

Looking at the list, can we make any generalizations about Iowa’s water?
Biological impairments are some of the most common impairments in Iowa streams and are due to unknown causes affecting the biological communities, altered habitats, low oxygen levels and siltation. In lakes, most impairments are due to turbidity (cloudy water), algal growth and excess nutrients.

When an assessment cycle shows more impaired waters than previous years, it does not necessarily mean that water quality has gotten worse in Iowa. It indicates that more monitoring has been done and more data has been collected than in previous years. It may also seem easy to compare the number of impaired waters to surrounding states. However, becausethere are so many varying factors in determining a state’s list, this is an inaccurate comparison, like comparing apples and oranges. Water quality in Iowa has also drastically improved since the advent of the Clean Water Act in the 1970s, which put controls on industrial and city sewage discharges into streams and rivers.

It’s been long enough since the Clean Water Act that many do not recall how poor water quality conditions were in the state before it, when raw, untreated sewage and other discharges went directly into our waterways. The state of Iowa’s waters is better now, but there is still work to do, including addressing pollution from non-point sources.

Non-point source pollution, especially sediment, nutrients and bacteria, washes into Iowa’s streams and lakes from farm fields, forested lands and urban areas. Those pollutants come from an area called a “watershed,” which is the area of land that drains into a lake or stream.

Pollution coming from non-point sources can be especially difficult to address. It requires efforts from many individuals within the watershed to reduce, slow and filter non-point runoff before it flows into a stream, river or lake. Progress is being made because, many Iowans are working hard to make changes on their land and in their communities that can improve water quality.

This page was created 5/26/2020 9:35:32 AM and was last updated 5/26/2020 10:50:19 AM