SRA Volunteers Track Severn River’s ‘Dead Zone’

Despite some great news about the Severn River this year – great clairty, abundance of underwater grasses – there’s bad news as well: Round Bay is also home to a permanent dead zone of water — very low oxygen levels.

WQ Crew Track ‘Dead Zone’ In Severn River

To track this phenomenon, SRA launched a river-wide Water Quality (WQ) monitoring program this year.

Every week, our WQ Crews track the advance of this dead zone, which now stretches from Ben Oaks at the top of the river all the way to the southern entrance, which we monitor as Round Bay South.

This so-called ‘dead zone’ is water with very low levels of oxygen (less than 3.0 mg/l).

It’s also inside many of our creeks: Chase, Brewer’s, Clements, Saltworks, Luce, Weems, Lake Ogleton and the upper reaches of Mills, Burley, Rideout and Whitehall Creeks.

Year-Round Phenomenon
Expands In Summer

This dead zone lies at the bottom of Round Bay all year round. It’s small in winter, but when summer rolls in and the river warms up past 80 degrees, the dead zone expands up and down the river.

It’s getting common this time of year to find horrible, horrible oxygen levels: 0.24 mg/l at our monitoring stations. This dead zone stretches along the bottom at 8 meters and is in spots 2 and 3 meters tall.

‘Dead Zone’ varies for different species

Various species can tolerate various levels of oxygen (see chart at left).

Four our tracking purposes, we’re primarily focused what’s stressful to oysters, which can’t swim away when bad water approaches.

According to DNR, anything less than 5 mg/l is stressful for oysters and hard clams.

For crabs, the level is 3 mg/l. Rockfish and White Perch need 5 mg/l or better to enjoy their habitat.

‘Way down on the bottom, worms can tolerate down to 1 mg/l oxygen.

Thankfully, Good News For Oysters

So far, the dead zone has not reached our oyster restoration reefs in the Severn River. We’re monitoring these restoration reefs every week.

If you’d like to help track conditions on the Severn River, we could a hand. Our WQ tours are Wednesday and Thursday mornings, usually 9 am to 1 pm.  To pitching, send an email to: and put WQ Crew in the message box.

If you don’t have time to join the tours, you can still support SRA’s water quality program by donating at: