Dead Zones

Photo by CBF Staff.Dead zones and algal blooms, which rob our waters of oxygen, often times result in devastating "fish kills" like these. Photo by CBF Staff.

"There were dead fish on the boat ramp eight inches thick. It's just awful." —Judy Bowie, Mattox Creek Homeowner

What are they?

Excessive nitrogen and phosphorus pollution from human activities cause "dead zones"—or areas with low amounts of oxygen in the Bay. With little or no oxygen, fish, crabs, oysters, and other aquatic animals literally suffocate. Further, an excess in these nutrients also fuels the growth of dense algae blooms that block sunlight that underwater grasses need to grow in order to continue providing food for waterfowl and shelter for blue crabs and juvenile fish.

What do they do?

Judy Bowie recounts a devastating summer just a few years ago when oxygen-deprived waters killed 296,000 fish in Mattox Creek, Virginia. Most of the dead fish were vital menhaden, white perch, and croaker; other species included gizzard shad, catfish, American eel, largemouth bass, and blue crabs. This particular "fish kill" resulted from a Potomac River algal bloom that quickly grew and extended more than 30 miles between Mathias Point and Nomini Bay at the Maryland-Virginia line.

When there are excessive loads of nitrogen and phosphorus in the water, algae can "bloom" to harmful levels, changing water color, and eventually stripping dissolved oxygen from the water when they die, fall to the bottom, and decay. This dissolved oxygen is critical to the health of Chesapeake critters and waters.

Where do excessive nutrients come from?

  • Wastewater treatment plants release treated water—often still containing large amounts of nutrients—into streams and rivers, which eventually flow into the Chesapeake Bay.
  • Runoff from farmland, urban and suburban areas empty into our streams and rivers carry nutrients from fertilizers, septic systems, boat discharges, and animal manure.
  • Air pollution from our cars, factories, gas-powered tools, etc. contribute nearly 30 percent of the total nitrogen load to the Bay's waterways.

What can we do about them?

  • Drive less, walk/bike more!
  • Don't over-fertilize your lawn (or don't fertilize at all!).
  • Grow oysters.
  • Buy local food.
  • Turn off the water when you brush your teeth!
  • Get more ideas here.
You may also be interested in:
  • Community Solutions to Addressing Polluted Runoff There are several proven strategies communities can implement to absorb runoff and reduce the risk of routine flooding and damage from polluted runoff.
  • Runoff: A Growing Threat Urban and suburban runoff is the only major source of pollution that is growing in the Chesapeake Bay and its rivers and streams.
  • Runoff: A Growing Threat Urban and suburban runoff is the only major source of pollution that is growing in the Chesapeake Bay and its rivers and streams.
  • The Gray Funnel of the Chesapeake Stormwater carries a host of contaminants from the land into the water: sediment, phosphorus, nitrogen, toxic metals, herbicides and pesticides, organic material, oil compounds, and bacteria.
  • A Little City with Big Plans to Minimize Stormwater Pollution On average each year about one billion gallons of sewage and stormwater-overflow pollute streams in Lancaster, Pa. Residents, businesses, local officials, and nonprofits have joined together to solve this problem.

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