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Mill Creek on the Magothy River had bacteria readings this week 34 times higher than levels considered safe for swimming, but other sites around the area were not too far behind, possibly because of a mild rain storm early in the week.

This is my weekly report of possible unsafe water in the greater Annapolis area. If you’re preparing to swim or come into contact with local creeks, rivers or in the open Chesapeake Bay this weekend, you might want to consider this information.

My map and the list of readings below can guide you, but here are a couple of the worst water areas in addition to Mill Creek: 1) Almshouse Creek on South River near the Pine Wiff community had bacteria readings 21 times higher than safe limits 2) Dividing Creek on the Magothy River had readings 16 times above safety levels 3) the Severn River at Hopkins Creek and near Olde Severna Park had readings eight times higher.

A storm on Tuesday night dropped  0.6 inches of rain. That might have elevated bacteria levels in the area, as runoff from storms tends to wash bacteria from animal and human waste into creeks and rivers. County and state health official caution not to swim or come into contact with water for 48 hours after a significant rain storm, least you risk health issues. Usually, those are mild, like getting sick to your stomach.  

Here are all sites where bacteria levels exceeded federal safety limits as of Wednesday’s tests. An explanation of the numbers, and further background appears below the numbers. Remember, bacteria levels can change dramatically within a few days, for better or worse, but you might think twice about swimming or coming into contact with water in these areas:

SEVERN

Old Severna Park – 850

Hopkins Creek – 874

Brown’s Pond – 138

MAGOTHY

Mill Creek – 3460

Dividing Creek - 1620

Magothy Manor – 134

SOUTH RIVER

Glen Isle – 104

Almshouse Creek – 2124

Selby Bay – 124

Broad Creek/South River Manor – 616

The acceptable level for swimming and other direct water contact is determined by the U.S. Environmental Protection Agency, Maryland Department of the Environment and the Anne Arundel County Department of Health. For bodies of water that the Department samples weekly and biweekly, the acceptable level of enterococci bacteria is 104 or fewer bacteria colonies per 100 milliliters of water. For areas that are sampled monthly, the acceptable level is 158 or fewer colonies per 100 milliliters. Each of the beaches above are tested each week. See Water Quality Fact Sheet.

Both the county health department and a network of volunteers test over 100 public beaches and other areas around the county for bacteria. The results from the county tests are put online here, and for the volunteer tests here for Severn and Magothy rivers, and here for South River. As of Thursday afternoon, the county officials had not posted their Wednesday readings, but volunteers had. I will try to update this report when the county catches up.

The county is good about posting signs if their inspectors find bacteria levels have climbed above federal safety limits. But you should also realize bacteria readings are almost always highest after a strong storm, and county water testers may not check at that time. So just because there’s no sign doesn’t mean the county has checked the area, and found it safe. The inspectors’ weekly or bi-weekly schedule may mean they arrive days after the water was bad.

The best rule of thumb—which the county makes clear on its website—is to avoid swimming or contact with “natural” water (not swimming pools) for 48 hours after a significant storm, say an inch or more of rain. That can be an average summer thunderstorm.