From the Arvada Press (Sara Van Cleve):
Because of the extreme heat this summer, several kinds of algae, specifically ceratium and gomphosphaeria, have sprouted in Arvada Reservoir. “It’s the extended period of it that’s causing it to grow,” said Wendy Forbes, communications manager for the city of Arvada. “There is not enough fluctuation in temperatures.”
As the algae dies, it releases into the water a harmless chemical that causes the change in smell and taste, Forbes said. Though some residents have tasted and smelled the algae’s effects in their water, Forbes said, it is completely harmless.
“Arvada Water is adding carbons to the system to help with some of that,” she said. “It should stop once the algae is gone.” It takes about four days for water to pass through the purification system completely, so it takes about that long to collect enough data to see if the extra carbon is helping.
More water treatment coverage here.