Microseira wollei, a toxin-producing cyanobacterium described in 1870’s, has emerged as a significant public health hazard in various freshwater habitats in the eastern U.S. The taxa has been observed in the tidal freshwater Potomac River for at least a decade, but has become very prevalent since 2000. This species appears to start forming mats in shallow areas, often under submersed aquatic vegetation and then sloughs off to form floating mats and distinctive balls of filaments. In 2024, drifting balls and mats were collected monthly at a littoral zone site on the tidal freshwater Potomac River near a large Vallisneria bed in the Tidal Potomac River for analysis. Growth potential as measured by C-14 uptake was combined with pigment, organic weight, and percent viable cells data to determine how these population characteristics varied seasonally. We hypothesized that this organism would be healthiest in the summer when temperatures were greatest and less healthy in the cooler months of the year. Healthy populations would be characterized by high rates of C-14 uptake per unit biomass, high ratios of pigments to organic weight and high percentage of viable cells. While there was viability in individual values, C-14 uptake showed a significant increase with increasing temperature in the period from June through December. Phycocyanin/chlorophyll a ratios were 12-14 and chlorophyll a/organic weight ratios were 0.02-0.05 with little seasonal change. The study will continue through an annual cycle.