Staff photo by REID SILVERMAN Kenny Kalan, center, of Hydrologic Data Collection in Alexandria, Va., sets up a dam monitoring system Friday at St. Mary's Lake along with electronic engineers Blaine van Dyke, left, and Faisal al-Mtwali of Sutron in Sterling, Va.

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An earthen dam holds back 250 acres of water upstream of Great Mills. Completed in 1975, the state built the dam to control flooding downstream. There was a similar plan to dam 307 acres of the eastern branch of the St. Mary’s River, but that fell apart part by 1984.

Up until last Friday, the only way to find out the water level of St. Mary’s Lake was to send Maryland Department of Natural Resources staff down to physically inspect it.

Now a $26,000 remote water level monitoring gauge has been installed on the side of the dam that local emergency officials can read remotely.

During Hurricane Irene last August, Park Manager Christy Bright had to check out the lake as it continued to rain and winds blew down trees that evening.

“Christy Bright had to cut her way with a chain saw back to Route 5,” said Bob Kelly, director of the St. Mary’s County Department of Emergency Management and Technology.

The depth of the lake rose to 68 feet as almost 12 inches of rain fell that day. At 70.5 feet, the lake rises onto an emergency spillway — a field next to the dam, and water pours into the western branch of the St. Mary’s River.

There are 65 properties downstream of the lake, including a low-lying trailer park on the St. Mary’s River at the end of Adkins Road in Great Mills.

“This’ll help a lot,” Bright said Friday as she watched workers of the Sutron company install the remote system. “It just keeps rangers out of harm’s way. That wasn’t a fun day,” during Hurricane Irene, she said.

DNR will still send someone out to assess the lake when storms hit, but the water level will be monitored at the county’s emergency management office in Leonardtown and at Bright’s headquarters at Point Lookout.

The dam was rehabilitated in 2008 after wet spots were first found in the winter of 2004. The lake was partially drained for years to keep the dam dry as the integrity of the dam was investigated.

The dam breast itself is 38 feet higher than the lake at the dam’s regular level and is 1,670 feet long. The dam is inspected annually and “is in excellent condition,” said David Decker, regional engineer for the Maryland Department of Natural Resources. “It’s functioning as it should. It’s a flood-control device.”

Great Mills still floods though because the other branch of the St. Mary’s River still flows through the area and quickly becomes a tidal river, he said.

There haven’t been any issues at the lake or dam this summer, Bright said, other than that it’s been too hot for fishing.

jbabcock@somdnews.com