Five Island Lake Assoc.


Since the Iowa DNR created the Impaired Waterways List back in 1998, Five Island Lake has been on it. A big problem facing the lake is the seasonal algae blooms that occur each year typically in the summer months. These blooms vary greatly in type, duration, and severity. Blooms can take the form of a green tint which limits water clarity or a large greenish slick across the surface, like a spilled bucket of paint. A lake’s ecosystem needs algae to survive, but it becomes a problem when there’s too much. Algae are tiny aquatic plants, and like all plants need nutrients to thrive. Algae becomes overabundant when the lake becomes eutrophic, meaning that there is too much phosphorous in the water. This problem is not unique to Five Island Lake, most of the waterways in the state experience eutrophic or high phosphorous conditions.

Phosphorous enters the lake from a variety of sources. In urban settings phosphorous comes from excess lawn fertilizer, golf courses, pet waste, and aging septic systems. Another significant source of these nutrients is agricultural activity. Most phosphorous is transported to the lake by the processes of erosion. Phosphorous particles stick to sediments that are either washed into the lake by runoff from heavy spring and summer rains or blown in by strong winds. This means that the best way to manage nutrients, like phosphorous entering the lake is to control erosion and runoff.

Erosion control can take many forms. On the farm, reducing tillage is the best way to keep nutrients, especially phosphorous, in the field. Converting to a no-till system can reduce phosphorous loss by 60%. Conservation tillage offers a reduction of 33% and adding cover crops to a farming system can have a 40% reduction. There are also edge-of-field and constructed practices like waterways, filter strips, and wetland restoration. More information about these practices can be found in Whole Farm Conservation Best Practices Manual, available for free from Iowa State Extension.

Erosion and runoff don’t just occur on the farm. Urban areas also contribute significant amounts of phosphorous due in part to their proximity to the lake. The best way to control phosphorous in an urban setting is to limit runoff and get rainwater to soak into the ground. Like the farm, there are conservation practices that can be used in your back yard. Practices like rain gardens, native plantings, and bioswales can filter nutrients and add beauty to yards and neighborhoods. Information about these practices can be found online at

by Warren Jennings, Watershed Coordinator

The FILA column will appear in local newspapers bi-monthly.


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