In Cincinnati for a wedding this weekend, I learned that the largest algal bloom in recorded history has developed on the Ohio River. Five hundred miles long, from Wheeling, West Virginia, to Louisville, Kentucky, a layer of blue-green algae on the river's surface is threatening wildlife and humans alike; toxins from the algae can induce a variety of ailments from mild rashes to liver damage. Fortunately, modern water treatment systems are capable of removing both the algae and the toxins, so the water supply of the larger cities is unaffected.
Algae blooms generally develop when water is nutrient-rich, excessively warm and relatively stagnant. In this case, nutrients are supplied by agricultural run-off and wastewater effluent; summer heating and relatively low rainfall throughout the Ohio River watershed has provided the warm, sluggish water. According to local hydrologists, the river flow is currently less that 0.25 mph (normal rates for this time of year range from 0.5 to 1.0 mph).
Depending on regional weather conditions, the massive algal bloom is expected to dissipate within a few weeks as the weather cools; of course, heavy rains in the Ohio Valley would also serve to disperse the algae. Until then, residents of towns and cities along the Ohio are advised to stay out of the river; unfortunately, wildlife species do not receive such a warning.
