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Mahogany Tide Staining Chesapeake Bay, Killing Fish By Thousands

BALTIMORE (WJZ)-- Fish kills in the Chesapeake's streams and rivers happen, but seldom this early.

As Alex DeMetrick reports, man and nature have worked up the perfect recipe for a die-off going on right now.

Waterways like Marley Creek on Maryland's Western Shore have been hit by algae blooms called mahogany tides, and it's been killing thousands of fish. They're dying from a lack of oxygen.

"Typically, it's at the end of creeks where you get this algae blooming, and it depletes the oxygen from the water," Pierre Henaart, a scientist with the Severn Riverkeeper Program, said.

That leaves dead zones, and death for animals trapped in them.

The Severn Riverkeeper Program routinely checks for those dead zones using underwater probes that measure dissolved oxygen at different depths.

"It's still going down. The oxygen levels are low here," Henaart said.

Here's why: Massive amounts of runoff from tropical storms last year carried huge loads of sediment containing nutrients like nitrogen, which feeds algae.

Satellite images showed the extent of that load. Then along with a warm winter, events like the major sewage spill in the Patapsco River hit in March.

"We're estimating, right now 55 million gallons," a Department of Public Works official said.

That's more food for algae, which expands in sunshine, but at night:

"It shuts down and actually has to metabolize and consume that oxygen," Henaart said.

To improve the water, it's all about making changes on land.

"Stopping the stormwater flow from the land along with getting our wastewater plants fixed," Fred Kelly of the Severn Riverkeeper Program said.

Because when enough nutrient pollution flows down stream and finds warm weather, it creates a perfect mix for death.

While mahogany tides aren't a risk to human health, in waterways like Marley Creek, bacteria levels from decaying fish have placed them off-limits to swimming and waterskiing.

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