Harmful Algal Blooms (HABs) are an escalating concern for both recreational and municipal water bodies. Driven primarily by nutrient enrichment and rising temperatures, HABs – caused by toxin-producing cyanobacteria – pose a significant threat to lake health, public safety, and water infrastructure.
Cyanobacteria are highly adaptable organisms that thrive in stagnant, nutrient-rich, and warm environments. As these conditions become more common, blooms are appearing earlier in the season, lasting longer, and covering larger surface areas. In many regions, what were once sporadic or seasonal events are now near-permanent features of the aquatic landscape.
According to Dave Shackleton, president of Clean-Flo International, a US-based leader in biological water management solutions for managing water quality, commonly held of misconceptions about how to manage algae blooms are effectively keeping lakes “sick” by facilitating the dominance of cyanobacteria and accelerating the deterioration of the lake’s ecosystem.
MISCONCEPTION: Chemical Applications Effectively Controls HABs
The most common conventional approaches to addressing invasive weeds and algae blooms typically rely on the use of treatment chemicals. However, biocides (herbicides and algaecides) as well as chemicals designed to reduce phosphorus levels accelerate the deterioration of the reservoir’s ecosystem while increasing the frequency and intensity of HAB events.
“By killing algae and cyanobacteria cells, toxins are released that lead to the destruction of more beneficial organisms,” explains Shackleton.
The dead algae cells also sink to the sediment and, as they decompose, recycle nutrients to fuel more algae blooms. This decomposition causes oxygen to be consumed in the water, leading to hypoxic conditions, or “dead zones,” where aquatic life cannot survive.
“Over time, the continued application of algaecides causes compounds the sediment nutrient stockpile at the bottom of a lake that are recycled to feed more algae blooms and shift the profile of the phytoplankton towards more and more cyanobacteria,” says Shackleton.
Alum and other phosphorus precipitants are chemical agents used to reduce the levels of Total Phosphorus, but “precipitants deposit phosphorus into sediment. When sediment is hypoxic, the microbiology changes and recycling of nutrients accelerates. Beneficial algae cannot access them there, because they can only float passively near the surface. Cyanobacteria can control their buoyancy and descend to the sediment to use those nutrients, so precipitating phosphorus into the sediment helps cyanobacteria become even more dominant over time,” says Shackleton.
MISCONCEPTION: There are No Visible Algae Blooms, So the Lake Must be Healthy
A common misconception in lake monitoring is the reliance on surface-level measurements of dissolved oxygen to assess overall water quality. While surface readings may appear normal, they provide no indication of the oxygen conditions at depth where the most serious problems originate. Hypoxia, or low oxygen levels, begins in the deeper layers of a lake due to decomposition of organic matter which causes sediment nutrient accumulation. These conditions go undetected when monitoring is limited to the upper water column.
MISCONCEPTION: Nutrient inflows are the primary problem
A common misconception is the belief that nutrient inflows from the watershed are the primary issue, and therefore, financial and operational resources should be concentrated exclusively on mitigating these external sources.
“That ship probably sailed 25 years ago,” says Shackleton. “In many lakes, it is the internal sources that contribute more nitrogen and phosphorus to algae blooms.”
The threat is from the decades of accumulated phosphorous and nitrogen stored in the organic sediment.
“These act like a high risk “time bomb” that is released under low-oxygen or stratified conditions, particularly during warmer months,” explains Shackleton.
MISCONCEPTION: A Good Trophic State Index (TSI) Score Means the Lake is Healthy
For the past five decades, the Trophic State Index’s (TSI) has served as a standardized eutrophication assessment, but it has significant limitations and redundancies, according to Shackleton.
The narrow emphasis on symptoms has led to many reactive, short-term actions such as the use of algaecides and phosphorus precipitants that temporarily improve TSI scores but ultimately worsen harmful algae blooms.
A more effective approach to assessing lake health involves quantifying the volume of hypoxic water to evaluate the extent of oxygen-depleted zones within the reservoir, combined with continuous phytoplankton monitoring to track the balance between beneficial algae and harmful cyanobacteria.
These factors can be systematically monitored using the Reservoir Risk Assessment and Tracking System (RRATS), which consolidates the data into a streamlined Reservoir Risk Index score.
“This score provides a clear and actionable indicator of a reservoir’s current risk status,” says Shackleton. “Only with this foundational understanding can lake managers effectively prioritize interventions, allocate resources strategically, and implement early risk mitigation measures.”
For more information, visit www.clean-flo.com; email contact@clean-flo.com; or call 1-800-328-6656.