ESSEX, MD—Following significant declines in nuisance midge levels along the Back River in eastern Baltimore County, County Executive Johnny Olszewski on Friday announced that midge reduction treatments will continue this spring. Aerial spraying – along with remediation inside Baltimore’s Back River Wastewater Treatment Plant – is expected to begin on Monday, March 4, and continue through the fall.

“We remain committed to ensuring those who visit, live and work along Baltimore County’s waterways are able to enjoy our amazing outdoor activities, and are encouraged by the positive results from midge treatments both on Back River and inside the Wastewater Treatment Plant,” said County Executive Olszewski. “I am grateful for the support of Baltimore City and our state partners on this quality-of-life and economic issue and look forward to continuing the program again this year.”

Expanding on successful efforts to treat the upper reaches of Back River with Bti, a naturally occurring bacteria found in soil, Baltimore County’s Department of Environmental Protection and Sustainability (DEPS) last year began coordination with Baltimore City Department of Public Works to apply the same natural larvicide to the wastewater at Back River Wastewater Treatment Plant prior to discharge.

Baltimore County has completed four in-plant treatments to date, along with applying Bti by helicopter to approximately 2,000 acres of the upper reaches of Back River from March through late September 2023.

Monitoring results through the 2023 midge season consistently showed midge larvae counts in the river well below the previously surpassed nuisance level of 500 per square meter, and in most cases below 100 per square meter. The most recent measurements last fall averaged 75 per square meter. Treatment and monitoring inside the wastewater plant continue year-round, as warmer water temperatures in the plant remain conducive for midge reproduction.

“It has made a huge difference, and we’ve very appreciative,” said Sam Weaver, owner of Weaver’s Marina in Essex. “It used to be absolutely terrible – I hadn’t been able to leave a window open for years, and you had to have bug spray by every door and spray just to walk outside.”

Since launching this effort in 2021, Baltimore County has seen major progress in combatting nuisance midge populations. For the past two years, Baltimore County and the Maryland Department of Agriculture have shared the $1.26 million annual program cost with the goal of reducing the midge population to tolerable levels.

Midges are small non-biting aquatic flies that often swarm near water or marshy areas where they breed, creating a nuisance for homeowners, boaters, businesses and recreational activities. Bti is a naturally occurring bacteria that is found in soil, and is only harmful to certain organisms, specifically midge, black fly and mosquito larvae and a few other aquatic flies. Bti does not harm people, fish, crabs or other aquatic invertebrates. The County’s contractor follows all applicable regulations and industry best practices.

More information about Bti is available on the Maryland Department of Agriculture website (PDF).

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