Giant Dead Zone Invades The Severn River

ANNAPOLIS (Sept. 12, 2019) –  There’s some sad to report: despite some great clarity and a bountiful crop of forage fish and underwater grasses this year, there is an extensive dead zone in the Severn River this summer.

A special report produced by the Severn River Association (SRA) uses data collected by the group’s water quality monitoring team to reveal the extent of the dead zone.

It is a vast stretch of water with very low-oxygen content that stretches from just above the Rt. 50 Bridge all the way up the river, into the creeks, through Round Bay and up to The Narrows.

It’s huge! It’s more than 5 square miles, roughly the size of Denton, Md.

In Figure 1 at left, the green area is the size of the dead zone in early June. The red outline is how big it had grown by mid-August.

The dead zone creates problems for the fishery because it forces fish and crabs to leave areas where they would normally inhabit. It is not a threat to humans, but it can suffocate aquatic creatures if they can’t swim away.

This calculation was produced by Mackenzie Miller, our summer intern and Field Investigator from Duquesne University working with data collected by SRA’s volunteer citizen scientists.  Mackenzie and her team of volunteer WQ Crew are collecting WQ data this year using a protocol approved by the Chesapeake Monitoring Cooperative, a division of the Alliance For The Chesapeake Bay. Mackenzie analyzed the WQ data to produce this Mid-Summer 2019 Report and calculate the size and location of the dead zone.

In the chart at right, produced by Izzie Ketcham, a Chesapeake Conservation Corps member now working with SRA’s Field Investigator, tracks what a dead zone looks like on a chart of oxygen content. This chart details the oxygen content of the water column on Aug. 21, 2019 at our monitoring station at the southern entrance to Round Bay.

The green line represents water with good oxygen content of 5 mg/L or more where fish can thrive.

The red line is oxygen at the 2 mg/L level that marks the dead zone level. Fish and crabs suffocate in water with this low oxygen content when they can’t move to better quality water.

The chart reveals that the bottom half of the river at this site is a dead zone for most aquatic life. The top half of the water column features good water quality with oxygen levels better than the 5 mg/L. This phenomenon is known as “hypoxic squeezing” that forces fish and crabs to concentrate in the surface of the river where there is sufficient oxygen to breathe – if they can tolerate the hot water temperatures that exceed 80 degrees Fahrenheit this time of year.

Note: The Dead Zone is not a threat to humans. It can be deadly to fish and crabs if they can’t escape the low-oxygen waters.

SRA’s Mid-Summer 2019 Report tracking the size of the dead zone is available here.