Sewage was flowing into Lake Washington all day Sunday because of a pump failure in Medina. Elsewhere, overflowing sewage flooded a yard in Mercer Island and closed two Seattle parks, said Annie Kolb-Nelson, spokeswoman for the King County Department of Natural Resources and Parks.

"During very severe weather, the conditions in the system can cause it to be overwhelmed," said Kolb-Nelson.

Seattle is especially prone to overflow problems, she said, because of old pipes.

Sewage began to overflow at the Medina Pump Station about 1 a.m. Sunday, and then a computer malfunction made the problem worse, according to a county news release. Crews began using manual pumps, but an unknown, "significant" amount of sewage was still flowing from the station directly into Lake Washington Sunday afternoon, Kolb-Nelson said.

Meanwhile, the Cascade Siphon in Renton was backed up and sewage was overflowing into the Cedar River.

Seattle closed Meadowbrook Park in North Seattle because of a pond that overflowed with sewage there, and crews closed Carkeek Park after a volunteer reported sewage washing across a trail Sunday afternoon.

On Mercer Island, an overtopped manhole sent sewage streaming into someone's yard, so the county called in cleaning crews.