You've chosen a lake,

now you can review lake conditions, check out blogs and other community submissions, and browse through lake photos.

Grand Lake St. Marys

Map via Ohio State Parks (

When completed in 1845 as a reservoir for the Miami-Erie Canal, Grand Lake St. Marys was, at 13,500 acres, the largest manmade lake in the world. Situated in western Ohio, it has an average depth of only five to seven feet. Grand Lake St. Marys is located on a major route for migratory birds. Waterfowl and wading birds are common, and bald eagles have recently returned to nest in the south western corner of the lake. On the eastern shore is the St. Marys Fish Hatchery. Run by the ODNR Division of Wildlife, the hatchery raises saugeye, walleye, channel catfish, and bass for stocking the state’s public fishing waters.

Open for year round recreation, Grand Lake St. Marys offers boating, fishing, swimming, hunting and camping. There are five public boat ramps and four public swimming beaches. Fishing on the lake is year round, and common game fish include bass, yellow perch, and bluegill. Additionally, the state of Ohio maintains 90 duck blinds in areas where hunting is permitted.

CyanoMap Report

Unfortunately, recent conditions in the lake have supported the intensification of annual harmful blue-green algae blooms, culminating in a series of advisories against contact with the lake’s water. Increasingly high levels of nutrient run off from farms, namely nitrogen and phosphorus, and other pollution encourage the blooming of cyanobacteria which produce toxins affecting the livers and nervous systems of those exposed to them. In 2010 a highly toxic bloom had chlorophyll-a levels over 25 ug L-1 and microcystins concentration exceeding 2000 ug mL-1 in some locations.

CyanoMap is collaborating with local universities and officials to measure cyanobacterial harmful algal blooms (CyanoHABs) using special data gathering equipment and custom remote sensing algorithms. This work includes sampling fish and testing for bioaccumulation and toxins. Laboratory testing for BMAA (beta-Methylamino-L-alanine, an amino acid produced by cyanobacteria) in fish tissue has come back positive, indicating this cyanotoxin is present and a potential health threat. While measuring water quality in situ at Grand Lake St. Marys, readings of 30+ ug / L were not uncommon and spikes upward of 140 ug / L have been recorded. CyanoMap staff are processing and analyzing Landsat, Proba, and MERIS imagery corresponding to field work and in situ samples. Lake level spectroradiometers were used to collect on lake, hyperspectral sensing data to help calibrate the remote sensing models used to monitor the water quality.

Landsat 5 image from June 19, 2010 (color adjusted to show detail)