Thousands of pounds of excess phosphorus wash into Geneva Lake every year, said Ted Peters, environmental agency director.

Peters said that from past observations, phosphorus causes sudden blooms of lake weeds and algae, clogging the shorelines and turning the clear waters of Geneva Lake green.

Geneva Lake has 5,426 acres of surface, and its surrounding watershed is 12,800 acres, with almost all of its open spaces developed into private lawns, golf courses or parks.

Peters said limiting phosphorus fertilizers probably would have little effect on lawns and fairways. Most soils in the Midwest have enough naturally occurring phosphorus for healthy lawn and plant growth.

William Chesen, a Lake Geneva alderman who first proposed a phosphorus ban for the city, said that as the lake vegetation dies, it creates a stink, particularly around the city’s west end pier.

And when water plants die, it leads to fish kill.

While a draft of the ordinance will be ready this winter, Peters said he doesn’t expect the new rules to take effect until 2008 to give landscapers, lawn care companies and home and garden stores a chance to empty their old stock of fertilizers.

Peters said he hopes to have a draft ready by the end of February.