12:58am: CNN reports that a damn in Maryland is at danger of being breached should heavy rains continue. The dam is St. Mary’s River at Great Mills. Weather Underground links to gauge showing the dam at 98% — far into the danger zone.

1:00am: Reviewing the larger map, check out the purple notes. Those represent dams over 90%. Some (like Chester Creek in Pennsylvania, Cashie River in North Carolina) are at critical stages.

1:03am: CNN covering the St. Mary’s dam now. A “Code Red” has been issued, meaning the dam could burst.

1:06am: And here we go from NBC News.

Due to the heavy rains from Hurricane Irene, St. Mary’s County issued a potential St. Mary’s Lake Dam failure notification.

People who live downstream from the dam are threatened by the possibility of significant flooding.

Residents in the area are advised to move family and pets upstairs.

1:13am: Jimmy Bise, based in Maryland and familiar with the area, weighs in:

FYI, St. Mary’s Lake, held back by the dam, is 250 acres big. If the dam goes, it could threaten at least a third of the county.

Note that Lexington Park, just east of the lake, has built up considerably as the Naval Air Station there expanded.

Interesting.

1:34am: A positive-but-not-wonderful update:

St Mary’s Dam owned by DNR near overflow. Emergency action plan being carried out. Level 2: notification. NOT Level 3.

MEMA trying to get a handle on St. Mary’s Emergency Mgmt on dam situation. MEMA checking to see if there’s any further threat.

MEMA working to determine where they will fly tomorrow morning to identify damage.

MEMA is the Maryland Emergency Management Agency.