The Department of Public Works began pumping about 30 million gallons a day from the river into the washwater lake at the Montebello treatment plant. The water is then mixed with supplies from Loch Raven and Prettyboy reservoirs and treated before distribution. The current blend is about one-third river water and two-thirds reservoir water, according to DPW.

The change is putting attention on two settling lakes at Montebello that have accumulated sediment and treatment-plant residue during years of delayed dredging. The washwater lake is full of residuals, while Lake Montebello is about one-third full, according to a DPW graphic presented to the Board of Estimates.

A dredging contract was approved in July 2026, but work is not expected to begin until the end of the year and could take two years. The lakes’ last major dredging dates back to 2007, according to the information provided by DPW and retired department engineer Robert Parks.

DPW says river water will first enter the washwater lake, then move to Lake Montebello to give sediment more time to settle before treatment. The department is also coordinating with the dredging contractor to install a sediment curtain to catch particles that remain suspended. DPW says the gradual blending should limit taste and odor changes and that the water will continue to be treated and tested against state and federal drinking-water standards.

Parks, who worked at Montebello for 37 years, said the old pipeline carrying river water from the Conowingo Dam to Abingdon has not been used since 2002 and may contain accumulated dirt and sludge. He expects residents could notice changes in color, taste or smell, though he said a blend with less river water should be less noticeable than the 50-50 mix used in 2002. DPW has said any odor or taste effects are expected to be minimal, if they occur.

More river water also means the plant’s filters may need more frequent backwashing, producing additional residue. DPW says it has lowered the washwater lake’s level to make room for incoming water, requiring more discharges through Tiffany Run, a stream that flows into Herring Run and ultimately the Back River and Chesapeake Bay.

Those discharges must comply with the plant’s federal pollution-control permit. The plant received five permit violation notices over the past year, according to Environmental Protection Agency records; the most recent, dated Aug. 28, concerned suspended solids and pH. Parks said keeping discharges within permit limits has long been a concern and argued that dredging is important to the plant’s operation.

The affected service area includes parts of the city and county east of Interstate 83 and communities east of Catonsville in South Baltimore. Western and northwestern areas will continue to receive water treated at the Ashburton plant from Liberty Reservoir.

The need for Susquehanna water could ease if substantial rainfall restores levels at Loch Raven, Prettyboy and Liberty reservoirs. Until then, DPW says it will monitor and treat the blended supply, while the delayed dredging leaves the Montebello plant managing river sediment with less settling capacity than planned.