It’s a familiar sight to residents living on the shores of Kitsap Lake in Washington: each summer, around the beginning of June, a bright green algae begins to creep across the water. These blooms can be harmful to people and pets and have forced closures of Kitsap Lake and its beaches every year for the last five years
This year, a different approach was taken. Starting in June, contractors sprayed the lake with a compound called Phoslock, which helps remove phosphorous from the water. Then an aquatic vegetation harvester trawled across the south end of the lake, chopping down underwater weeds and hauling them to shore. The goal – to remove as much phosphorous from the lake as possible.
Sediment in the lake – from decomposing weeds, lawn fertilizer, stormwater runoff – produces excess phosphorous, which acts as fuel for algae blooms. Relatively few outflow points on the lake result in a slow turnover rate of water and poor nutrient cycling, according to a 2011 Kitsap Public Health District report.
The harvester removes plant life and opens the water up to circulation, allowing for the water to mix and more sunlight to reach the deepest parts of the lake.