A newly opened wetland complex just south of the St. Marys River is pulling the vast majority of phosphorus and nitrogen out of nutrient-laden canal water before it can flow toward Lake Erie. The project, built on a 64-acre property at 12654 Aqueduct Road, uses 31 acres of constructed wetlands to intercept runoff from the historic Miami-Erie Canal, filter it through a series of pools, and release cleaner water back into the canal and the adjacent river.
The site is officially named the Pat McGowan Treatment Train, honoring the former St. Marys mayor who led early municipal efforts to secure the land, according to The Daily Standard. The Ohio Department of Natural Resources and its H2Ohio program partnered with the city of St. Marys on the project, celebrating the opening of the new water treatment system as part of a broader push to reduce nutrients flowing northwest past the city, according to a post from the Ohio Department of Natural Resources on Facebook. Nutrient flows that pass through the site ultimately enter the Maumee River and, eventually, Lake Erie itself, per the same post.
Two Years of Testing Show Sharp Nutrient Cuts
Early monitoring data presented by Dr. Stephen Jacquemin during two years of testing at the treatment train found an 82% reduction in phosphorus levels and a 68% reduction in nitrogen levels in the treated water, as reported by LimaOhio.com. That independent monitoring was conducted through the state's academic research consortium, the outlet notes. The wetland pool complex, also called a treatment train, is designed to systematically strip nutrients before discharging cleaner water back into the canal and the St. Marys River.
The project fits into a much larger statewide effort. Since its establishment in 2019, ODNR's H2Ohio wetland program has implemented more than 500 natural-infrastructure projects encompassing nearly 20,000 acres of ecosystem restoration statewide, according to the Ohio Department of Natural Resources. To independently evaluate how well these wetlands perform, ODNR contracts with the Lake Erie and Aquatic Research Network, a consortium of researchers from more than 20 Ohio universities that conducts ongoing water-quality sampling across 45 H2Ohio wetland sites, per Ohio Sea Grant.
Why Northwest Ohio Lost Its Natural Filters
More than 90% of northwest Ohio's original native wetlands were drained and filled over the past two centuries due to agricultural conversion and urban development, according to the U.S. Environmental Protection Agency. That loss of natural filtration is part of why engineered projects like the St. Marys treatment train have become necessary. Regional pressure to cut nutrient pollution intensified after the August 2014 Toledo water crisis, when a toxic microcystin algal bloom at Lake Erie's municipal intake forced a three-day drinking water ban for more than 400,000 residents, according to EnviroScience.
Those pressures now carry binational weight. Under Annex 4 of the U.S.-Canada Great Lakes Water Quality Agreement, environmental authorities set a mandatory target to reduce total phosphorus inputs into western and central Lake Erie by 40% from 2008 levels, per the EPA. Nearby Grand Lake St. Marys has suffered from chronic and severe cyanobacterial algal blooms for decades, forcing municipal drinking water utilities like the city of Celina to adopt specialized dissolved air flotation technology to remove microcystin toxins, according to Ohio Sea Grant.
Wetlands Pay Off Beyond Water Quality
A 2026 economic report published by Earth Economics and The Nature Conservancy calculated that H2Ohio's wetland restoration initiatives generated nearly $300 million in economic benefits across more than 180 completed sites, delivering an $8 return for every $1 invested, according to The Nature Conservancy. The St. Marys wetland's goal, as described in the ODNR's Facebook post, is to improve water quality throughout the region, adding one more treatment train to the growing statewide network aimed at protecting Lake Erie from the kind of nutrient loading that has plagued it for decades.
Hoodline has previously covered related efforts to address legacy pollution in the same watershed, including a $37.6M cleanup downstream on the Maumee River. Whether St. Marys' 82% phosphorus reduction and similar wetlands elsewhere can collectively meet the Great Lakes Water Quality Agreement's 40% target remains an open question that depends heavily on voluntary agricultural practices upstream, a challenge that stretches far beyond any single treatment train.
