Broken Stream Banks

Failure to maintain buffer zones worsens farm pollution

April 25, 2014

Broken Stream Banks: Executive Summary

Download PDFWater pollution from farmland is a major but largely preventable problem in southern Minnesota and wherever row crops dominate the landscape across the United States. Much of this pollution can be prevented by the conscientious use of riparian buffers - strips of grass, trees or other permanent vegetation maintained along the banks of rivers, streams, lakes and other waterways.

Minnesota's shoreland management rules require installation and protection of 50-foot wide riparian buffers between cropland and public waterways. These progressive requirements, which are rare in large agricultural states, confer legal protection on shoreline buffer zones that play a critical role in reducing polluted runoff and restoring broken stream banks.

Like any other law, however, it must be enforced to be effective.

Using a combination of high-resolution aerial photography and the Minnesota Public Waters Inventory (PWI) GIS data layer, EWG found that while numerous agricultural landowners maintain the required 50-foot riparian buffers along perennial rivers and streams, many others do not. Healthy, effective vegetative buffers are even scarcer alongside smaller waterways – public drainage ditches and intermittent streams.

This is bad news for water quality in southern Minnesota. The good news, however, is that better enforcement of the shoreland management rule offers a remarkable opportunity to help clean up southern Minnesota’s troubled waterways.

Perennial Rivers and Streams

EWG’s analysis found that only 18 percent (87) of waterways adjacent to cropland earned an A grade – meaning that 100 percent of the acreage within 50 feet of the stream bank was covered by the required buffers, while 21 percent (101 waterways) got a failing grade – meaning less than 60 percent of the required buffer acres was present. Another 14 percent (66 waterways) earned a D because only 60 to 69 percent of the buffer acres was maintained. Combining the highest and lowest grades, 30 percent earned an A or A- (90 to 99 percent of buffers acres in place), while 35 percent earned a D or F.

Watershed Map
See interactive map
Perennial rivers and stream are far better protected in some watersheds than in others. Click on the map to see how well stream banks are protected in your area.

In some cases, it was obvious that eroding stream banks were cutting into what might once have been an adequate buffer. Most of the time, however, there was no obvious explanation for the striking differences in the widths of the buffer zones other than uneven management practices of the landowners or operators involved. In fact, EWG’s analysis found a jumbled pattern – evident in this interactive map – in which watersheds and waterways that earn top grades are frequently next door to areas with failing grades.




Small Perennial Streams Hard Hit

Although small perennial streams amount to 31 percent of the miles of waterways EWG evaluated, they account for 45 percent of the total acreage of missing buffer zones.1 Large rivers and streams make up fully 48 percent of total waterway miles but account for only 28 percent of the missing buffer acreage. Where cropland has encroached on the protected zone, what remains of the buffer tends to be far narrower than the required 50 feet.

This is particularly bad news for southern Minnesota’s water quality. Smaller streams are more intimately connected to agricultural land than larger rivers, and buffering them has the largest impact on reducing polluted runoff.

Drainage Ditches and Intermittent Streams Are The Hardest Hit

EWG analyzed a sub-sample of the seven watersheds in southern Minnesota that have more than 20 miles of public drainage ditches associated with cropland, along with three watersheds that have more than 30 miles of intermittent streams in the Inventory’s GIS layer. EWG found that, on average, 99 percent of the 16.5 feet of buffer required by Minnesota drainage law was present along th public ditches we assessed.  In contrast, just 55 percent of the acreage within 50 feet of the ditch banks was buffered – a failing grade under the far more protective shoreland management rule. Five of the seven watersheds we investigated also got a failing grade. The other two earned a D and a C.

Intermittent streams in the Public Waters Inventory GIS layer present an even more troubling picture. Many of the waterways classified as intermittent have been plowed over and are now part of a field of row crops. Some of these intermittent streams are well buffered, while others have a grassed waterway that follows the course of the stream. But many have no protection at all.


Southern Minnesota and the Minnesota River basin in particular face serious problems with pollution by sediment and nutrients. These problems cannot be solved unless polluted runoff from cropland and stream bank erosion is dramatically reduced. Row crop agriculture must play a leading role in cleaning up southern Minnesota’s waterways. In 30 counties, row crops occupy more than 50 percent of the total land area, and in 13 counties row crops account for 75 percent or more.

Maintaining a buffer of permanent vegetation between row crops and waterways will not solve all of the pollution problems in the basin. But science and professional experience show that such buffers make an important contribution to cleaner water and stronger stream banks.

Minnesota’s progressive shoreland management rule presents a remarkable opportunity to accelerate progress toward cleaner water. Many agricultural landowners are maintaining the required buffers between cropland and waterways, but others are not, even along perennial rivers and streams. A concerted effort by state and county governments to ensure that the required buffers are in place would be an important step forward in harmonizing agricultural production and clean water in southern Minnesota. Better enforcement would ensure that the water quality gains achieved by those landowners who do comply with the agricultural buffer requirements are not undone by the poor performance of others – often their neighbors – who do not.

Some counties and local organizations have already stepped forward with initiatives to make sure that landowners understand their obligations under the shoreland management rule and ensure that those obligations are met. Our investigation shows, however, that much more needs to be done.

EWG hopes our report will contribute to that important work.

1 EWG divided perennial rivers and streams into three classes based on length. We classified waterways longer than 50 miles as "large," those 25-to-50 miles long as "medium," and those 1-to-25 miles long as "small."