Source: sightline.org

One Coho salmon does a flopping dance of death atop the creek’s surface. Another swims in dazed circles, then limply drifts downstream. A third lies on its side, mouth gaping open and shut, fins splayed. In Seattle’s Longfellow Creek, researchers at the Northwest Fisheries Science Center found that nearly four out of five female fish died with a belly full of eggs, perishing before they could spawn.

The culprit in this story is the most mundane of villains: the rain. As rainwater streams off roofs and over pavement, it mixes a toxic cocktail of oil, grease, antifreeze, and heavy metals from cars; pesticides lethal to aquatic insects and fish; fertilizers that stoke algal blooms; soap; and bacteria from pet and farm-animal waste. A heavy rainfall delivers this potent shot of pollutants straight into streams and water bodies—threatening everything from tiny herring to the region’s iconic orcas.

Stormwater doesn’t match the traditional image of pollution. There are no factory smokestacks belching waste, no pipes with a steady trickle of noxious effluent. Despite appearances, stormwater packs a wallop.  Runoff from streets and highways long ago surpassed industry as the number one source for petroleum and other toxic chemicals that wash into the Northwest’s rivers, lakes, and bays. Today, scientists fear that if runoff pollution continues unchecked, it could wipe out some of the region’s urban and suburban salmon runs.