A proposed citywide ban on the sale and use of fertilizers containing phosphorus could help clean up the algae problem plaguing Lake Mendota.

“The intent of the phosphorus ban is to reduce the frequency of the nuisance algae blooms,” said Susan Jones, Watershed Management Coordinator for Dane County.

Jones went on to explain that the decay of the algae creates the pungent smell that often deters people from visiting Lake Mendota. The decaying algae also deplete oxygen, hurting the fish population. Water clarity is also reduced.

The use of phosphorus-containing fertilizers on county-owned lands was banned on July 10th of this year. Currently, the Dane County Lakes and Watershed Commission is working with the County Board on an all-encompassing countywide ordinance halting the use of phosphoric fertilizers.

The Wisconsin Department of Natural Resources wrote a letter in July backing the county’s efforts to improve water conditions.

“Banning phosphorus fertilizers on lands such as residential lawns and golf courses will not be the panacea to improving the water quality of these lakes, but it is one of many steps that can be taken easily and inexpensively to provide load reductions to the lakes,” said Todd Ambs, Administrator of the Division of Water at the DNR.

Ambs said the majority of phosphorus coming into Lake Mendota is from agricultural sources, but 25 percent of the load comes from existing urban areas and construction sites.

Carolyn Rumery-Betz of the Bureau of Watershed Management at the DNR said she had some doubts concerning the effectiveness of the city’s ban.

“I don’t realistically think it will make a big difference because the large majority of phosphorus in the watershed is from agricultural sources,” Rumery-Betz replied.

She was optimistic, however, with some of the other city efforts that include street sweeping and leaf pick-up which also reduce phosphorus run-off.

Like the county’s proposed ban, the city of Madison’s proposed ban would not include agricultural land, which is covered under state law. In the city of Madison ordinance, city parks will be able to use fertilizers containing phosphorus if an area needs it because of damage or overuse. Golf courses under the direction of a Golf Course Groundskeeper would also be exempt, along with landowners planting turf via seed or sod during the first growing season.