Nutrients in Runoff Feed Excessive Growth of Algae in Lakes, Streams

Minnesota Pollution Control Agency News Release, Tuesday, August 14, 2007

Contact: Forrest Peterson, 320-214-3789

St. Paul, Minn.—Recent reports of dogs dying from blue-green algae in Minnesota lakes are drawing attention to the causes of algae blooms—the stuff that turns the water in many lakes various shades of green in the summer. Most of the 7,000 or so types of algae are not toxic, but in large amounts some forms can pollute lakes, rivers and streams.

Algae vary in size from small, single-cell forms to giant sea kelp. Without algae on earth for the past three billion years, life would not exist as we know it today. Algae comprise much of the food source for aquatic organisms and produce oxygen that enriches both the water and air. Excessive algae, however, is usually the most visible result of water pollution, floating on lakes like a smelly green blanket.

One of the forms, blue-green algae, produces toxins that can affect humans and animals. It can be fatal to animals and birds that ingest large amounts. In contact with humans, it can cause skin and eye irritations, or stomach ailments if swallowed. More information about toxic algae is available on the Minnesota Pollution Control Agency's (MPCA) Web site www.pca.state.mn.us/water/clmp-toxicalgae.html.

"We're taking a lot of calls about blue-green algae, and in some areas it's pretty severe," says Steve Heiskary, MPCA lake scientist. "The heat is allowing blue-green to really flourish by providing prime conditions to use the available nutrients. While more severe in high-nutrient shallow lakes, it's even affecting some of the better quality lakes."

Tom Bonde notices the difference in Green Lake at Spicer in central Minnesota where he returned after retirement as a fisheries scientist and water quality specialist for the U.S. government. Relatively deep and covering nearly 5,585 acres, Green Lake's reputation for clean, clear water is being challenged by increasing algae blooms, and also Eurasian milfoil.

"I remember the lake back in the '40s and '50s when even during the "dog days" of summer the water remained clear compared to other area lakes," Bonde says. When he returned to the family cottage on the west side, "the water quality changes were evident." Algae coated the rocks "a lot worse than I remembered," Bonde says.

During one of the recent hot weather spells Bonde noticed an algae bloom along the southeast shore near Spicer. "I took a sample to the DNR office and we tentatively identified four blue-greens. It stayed around for two to three days. I've never really seen it that bad in Green Lake. We've seen blooms before but it's the first time we've seen them come into shore."

At Little Rock Lake in Benton County, a large toxic algae bloom also raised concerns about air quality in the immediate area. At July 30 meeting with state and local officials and lakeshore owners, MPCA staff reported on the results of air and water monitoring. "Most recognized that there are no immediate 'quick fixes' to dissipate the algae bloom, and focused on long-term solutions to reduce the excess nutrients in the lake," said Shannon Lotthammer, manager of the MPCA water monitoring section.

Just like flowers in a garden or crops in farm fields, water, warmth and food nourish the growth of algae. In lakes there's plenty of water, and in summer we all enjoy the sun's warmth. The deciding factor in the amount of algae in lakes lies in the amount of "food" they get—primarily nitrogen and phosphorus. These nutrients come from many sources, which exceed natural conditions due to human activity.

As in leaves or grass, chlorophyll gives algae its green color. Algae use chlorophyll to capture energy from sunlight to feed on surrounding nutrients. How we fertilize lawns, maintain septic systems, treat wastewater, develop our lakeshores and run our farms and businesses can make the difference between a green lake and a clear lake. "It takes the concerted efforts of state agencies, local government, non-profit groups and individual citizens to help keep these excess nutrients from entering our waters," says Lotthammer.

In the late 1960s, researchers discovered phosphorus to be a major cause of algae growth and degrading lake water quality. It arrives lakeside via point sources such as wastewater treatment plants, and nonpoint sources including runoff from farm fields, lawns and streets. And it stays around for longer than anyone understood in those early days.

"While we have long recognized the impact of excess phosphorus and nitrogen on lake water quality, we did not have enforceable water quality criteria (standards) for the protection of lakes," says Heiskary. "The MPCA is in the process of developing nutrient criteria, in conjunction with a nationwide federal effort, to protect lake and stream water quality."

Public hearings on proposed updates to water quality standards rules including excess nutrients in lakes are scheduled to begin Aug. 29. Additional details about meeting start times and directions to all offices listed above are available on the MPCA Web site at www.pca.state.mn.us/water/standards/rulechange.html.

• Wednesday, Aug. 29 and Thursday Aug. 30—MPCA St. Paul office, 520 Lafayette Road North, St. Paul.
• Tuesday, Sept. 4—MPCA Duluth office, 525 Lake Avenue South, Suite 400, Duluth.
• Wednesday, Sept. 5—MPCA Brainerd office, 7678 College Road, Suite 105, Baxter.
• Thursday, Sept. 6—MPCA Detroit Lakes office, 714 Lake Avenue, Suite 220, Detroit Lakes.
• Tuesday, Sept. 11—MPCA Marshall office, 1420 East College Drive, Suite 900, Marshall.
• Wednesday, Sept. 12—MPCA Rochester office, 18 Wood Lake Drive Southeast, Rochester.
• If necessary: Thursday, Sept. 13—MPCA St. Paul office, 520 Lafayette Road North, St. Paul.

All interested persons or groups are invited to attend one or more of these public hearings. All MPCA offices can also be reached toll-free at 1-800-657-3864.

The mission of the MPCA is to work with Minnesotans to protect, conserve and improve our environment and enhance our quality of life.