Iowa DNR

Water Quality Assessments

Impaired Waters List

Understanding Impaired Waters

You’ve likely heard of Iowa’s many “impaired” waters. As the DNR 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.

Lakes and stretches of streams and rivers in Iowa each have specific designations, based on what they are used for—recreation, such as swimming or fishing; drinking water; or maintaining a healthy population of fish and other aquatic life. Every two years, Iowa must report on its progress in meeting water quality goals to the U.S. Environmental Protection Agency. The state prepares a report, called the 305(b) assessment, that shows how well Iowa waters are meeting those goals. The report includes waters that meet the designated uses, waters that we need more information about and waters that are impaired.

If the water quality in the stream or lake prevents it from fully meeting 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 referred to 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 (also known by a technical name, “Total Maximum Daily Load,” or “TMDL”).

The water quality improvement plan outlines water quality problems, identifies sources of the problem, identifies needed reductions in pollutants and offers possible solutions. Water quality improvement plans are approved by the U.S. Environmental Protection Agency and then the waters are moved off the 303(d) list.

Even though a water moves off the 303(d) list, the waterbody is still considered impaired until water quality improves and an assessment shows it meets water quality standards.

While the water quality improvement plan can offer ideas for solutions, and the DNR can provide technical or financial assistance for Iowans looking to organize a watershed improvement effort, 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.

What is a waterbody?

For the impaired waters list, waterbodies are defined as Iowa lakes, rivers, streams and wetlands that have assigned water use designations. When it comes to streams and rivers, they are split into segments based on different designated uses. For example, a segment of the Cedar River near Cedar Rapids is designated for drinking water, while a portion of the same river near Waverly is protected for other uses. If one segment is impaired, that does not mean the entire stream or river is impaired. However, improving the entire watershed, or area of land that drains to the stream, can have an impact on water quality in the impaired segment.

Not all waterbodies in Iowa are assessed every cycle, because water quality monitoring has not been conducted on many of our lakes and streams. Consequently, we don’t have the information to determine whether they are impaired or not. There are also many waterbodies, especially the headwaters of streams and small wetlands, that are not delineated and assigned assessment segments. 

What does “impaired” really mean? Is the water unsafe?

A waterbody is impaired when its water quality does not fully support that waterbody’s designated uses for human contact, aquatic life 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.

“The majority of impairments in Iowa waters are minor to moderate. Iowa’s water quality standards are designed
to alert us to a potential problem before serious pollution problems begin. For the most part, when a water is impaired, it tells us that we, as Iowans, need to act before those problems become severe." -- John Olson, Iowa DNR

Why don’t waters meet designated uses?

High bacteria levels indicate potential health risks for those swimming, wading and playing in the water. Excess sediment and nutrients, such as nitrogen and phosphorus, can reduce water clarity and increase algae, making it difficult for fish, plants and other aquatic life to thrive. As for drinking water, high levels of nitrate and other chemicals often call for additional treatment and higher costs. For example, the Des Moines Water Works built the world’s largest nitrate removal facility because of extremely high nitrate levels in the Raccoon River, one of its sources for drinking water.

If a water doesn’t meet its designated use for recreation, is it unsafe?

In most cases, an impairment indicates that there is a minor to moderate problem and that we need to address it before it becomes severe. However, there are some waters in Iowa with serious pollution problems. Water quality at Iowa’s state park beaches is generally good, as levels of indicator bacteria in samples collected during the summer recreational season have exceeded state standards only about 10 percent of the time since monitoring began in 2000. However, even when bacteria levels are high, the fish are safe to eat when properly cooked, unless the waterbody has a listed fish consumption advisory. Only a few lakes and river segments have current fish consumption advisories.

What do the impairments mean?

Waterbodies can be impaired because water monitoring shows high levels of pollutants, like nutrients, sediment or chemicals. Streams and lakes can also be impaired when biological monitoring finds that fish and other aquatic life populations aren’t as diverse or numerous as they should be.

By looking at the types and numbers of species, including fish, plants, insects and other aquatic creatures, scientists can make conclusions about water quality. The presence of certain species, especially in high numbers, indicate good water quality, while other species can tolerate higher levels of pollution. Investigators also look to see if species are stressed or diseased.

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.

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

What does the list say 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. Because there 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 of us don’t recall how poor water quality conditions were then, with raw, untreated sewage and other discharges going directly into our waters,” Olson said. “Our waters are much better now, but we still have 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 an area of land that drains into a lake or stream.

"When pollution comes from non-point sources, it can make it difficult to address. However, there are things we can do – and many Iowans are doing – to reduce, slow and filter non-point runoff before it flows into a stream, river or lake," said Bill Ehm, who heads the DNR's Environmental Services Division. “We are making progress as many Iowans are working hard to make changes on their land and in their communities that can improve water quality."

Do any waters ever come off the list?

Most waterbodies 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 problems in our state didn't happen overnight, so improving our waters requires a long-term approach,"said Ehm. "Iowans have come together on local watershed improvement efforts, and we're seeing improvements."

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.

Through efforts like these, the DNR and many Iowans put great effort into maintaining our high quality waters to ensure they don’t reach the impaired waters list.


This page was created 2/6/2018 2:38:51 PM and was last updated 2/6/2018 2:39:56 PM