ISU projects that phosphorus loading to the lake could be reduced up to 50-60% by implementing practices designed to address these issues. This would lead to a substantial increase in water clarity.

Decreasing the transport of phosphorus and eroded soil into the lake is critical to improving the health of the lake. Many conservation practices that address this issue are already in use in the Clear Lake watershed. Contour farming, terracing, and grass waterways are best management practices (BMPs) that are presently in use in the Clear Lake watershed. Many farmers are using field management methods that help to reduce phosphorus losses. However, soil samples indicated that there are fields in the watershed that contain much higher levels of phosphorus than what is necessary for maximum crop production. This excess phosphorus will be transported to the lake especially from areas with high slopes. AGNPS computer modeling was used to predict which portions of the watershed are supplying the most phosphorus to Clear Lake. The model predicted that placing the highest 10% of phosphorus exporting agricultural land in permanent vegetation could yield an average reduction in phosphorus load to that lake of around 8%.

To further reduce the amount of farm field nutrients from entering Clear Lake, ISU recommends that wetlands be restored in strategic areas. Wetlands and other small impoundments are known to immobilize significant amounts of sediments and nutrients in agricultural watersheds and the abundance of hydric soils in the Clear Lake watershed suggests that wetlands were quite abundant prior to human habitation. When combined with idling 10% of the agricultural land, these changes represent an 18% reduction in the total phosphorus load to Clear Lake.

Urban areas provide the most nutrients to Clear Lake on a per-land-area basis. Thus, ISU recommends that improved stormwater management, appropriate disposal of pet and yard waste, limiting the use of products containing phosphates, regular street cleaning, and improved construction practices should be implemented in urban areas.

Like wetlands, marshes are ideal for removing nutrients and sediments. Unfortunately, due to a variety of factors, Ventura Marsh has been providing nutrients and sediments to Clear Lake rather than filtering them out. To reverse this trend, ISU has recommended the following actions be taken to restore Ventura Marsh.

When combined with the watershed modifications and wetland installations discussed above, a 26% reduction in the phosphorus load to Clear Lake is achieved.