The 2015 Ohio River harmful algal bloom or HAB was first identified on August 19 and was reported as a paint spill around Wheeling, WV at river mile 84. The description of a paint spill is not uncommon, as the algal bloom can have a swirling visual effect. On August 20, the report was confirmed to be algae of a type capable of producing toxins. Samples taken August 21 between river miles 65-94 indicated toxins were below detection.

The bloom progressed rapidly down river with sampling between miles 55 and 126 taken on August 26-27 and visual observations at mile 161. On August 28, 3 million cells per liter were identified at mile 341 (Greenup). By September 1, the bloom was observed in Cincinnati; by September 7, the bloom was almost to Louisville. On September 21, it was observed at Cannelton at mile 720. Localized algae were observed near the Evansville water intake at mile 791 on September 28 and in clarifying ponds in Henderson.

The HAB is a concern because of the potential for release of toxins in the water supply and the potential harmful impact on livestock and possibly people. No documented human deaths have been recorded as the result if a HAB although livestock and small animals have been killed. Generally skin contact is not a great issue as the toxins generally have to be ingested to impact humans or animals. Human impact is generally manifested as flu-like symptoms, although neurotoxins can result in impact to memory and balance. Generally the liver is the most impacted organ. Several types of bacterial algae have the potential to produce several types of toxins. Importantly, these bacterial algae are present in the water at all times; it is the development of a large bloom that remains somewhat mysterious as to the triggering cause.

A prior Ohio River HAB was documented in 2008 around the Cincinnati area which lasted 10-14 days. Generally, HABS are more commonly identified in ponds and lakes, both small and large. In 2014, a large HAB was observed in the western portion of Lake Erie. Interestingly, two separate areas of the HAB were populated with different bacterial algae strains.

A number of factors are considered to be contributors to an algal bloom, including nutrients, temperature, and turbidity. Algae feed on light (photosynthesis), CO2, nitrogen and phosphorus, among other nutrients. Apparently alkalinity and hardness are also influencers. It is important to understand what we do NOT know as much as what we do know. The knowledge gaps include an understanding of what variables contribute to a HAB and an understanding of their interaction. The impact or contribution of river tributaries is unclear. Are they a source or a mitigating factor? What is the role of the USACE reservoirs?

This year, we experienced an extremely wet late spring and early summer with a very dry late July and August. However, nutrient levels were no higher than normal.

There is an effort among the Ohio River states to develop adequate information to inform a predictive model to identify when conditions are right for development of HABs. It is clear that capability does not exist at this time.

It is likely that the follow-up to the HAB will drive more pressure on nutrient loading as there is little means of controlling other factors which appear to be contributory. This will likely impact both agriculture and waste water treatment facilities as they are either the primary sources of nutrient loading or the perceived primary sources. Waste water treatment facilities will have permit limits reduced and agriculture will see additional pressure for buffer zones, testing and other limits.

For more information, contact Sara Smith at