Ecology
Hypereutrophic
A lake classification indicating excessive nutrient levels, very poor clarity, and persistent algae blooms, the most impaired category.
Hypereutrophic is a term from limnology — the scientific study of inland waters. The detailed explanation below covers the definition, why the concept matters to lake water-quality interpretation, and how it intersects with the LakeGrade rubric. Reading Hypereutrophic alongside the LakeGrade rubric helps make the rubric's structure intuitive — each grading parameter maps directly onto an established limnological concept.
The per-lake pages on LakeQuality always show the specific Hypereutrophic value for that lake, so you can move from the general concept to the specific lake without leaving the site.
What It Means for Your Lake
Hypereutrophic lakes represent the most nutrient-enriched and impaired category, with a Carlson Trophic State Index exceeding 70. These lakes have total phosphorus above 60 ug/L, chlorophyll-a above 30 ug/L, and Secchi depth typically below 3 feet, often less than 1 foot during peak summer conditions. The water is intensely green, and thick algae scums frequently cover portions of the lake surface. Cyanobacteria (blue-green algae) dominate the phytoplankton community and may produce toxins (microcystins and anatoxins) that pose health risks to humans and animals. Approximately 10% of monitored lakes in Minnesota and Wisconsin are classified as hypereutrophic. These lakes are concentrated in the heavily agricultural regions of southern and western Minnesota, the Minnesota River basin, and parts of south-central Wisconsin. Many are shallow prairie lakes that have always been naturally productive but have been pushed to extreme levels by agricultural nutrient loading and urban stormwater. Swimming and body-contact recreation in hypereutrophic lakes is strongly discouraged and may be prohibited during bloom events. Fish communities are typically dominated by rough fish species like common carp and bullheads, though some hypereutrophic lakes maintain channel catfish and black crappie populations. Restoring hypereutrophic lakes is extremely challenging because internal phosphorus loading from nutrient-rich bottom sediments can sustain poor conditions for decades even after external inputs are reduced.
Frequently Asked Questions
What is hypereutrophic?
A lake classification indicating excessive nutrient levels, very poor clarity, and persistent algae blooms, the most impaired category.
Why does hypereutrophic matter for lake health?
Hypereutrophic lakes represent the most nutrient-enriched and impaired category, with a Carlson Trophic State Index exceeding 70. These lakes have total phosphorus above 60 ug/L, chlorophyll-a above 30 ug/L, and Secchi depth typically below 3 feet, often less than 1 foot during peak summer condition...
Related Terms
Trophic State Index
The Carlson Trophic State Index (TSI) is a numerical scale from 0 to 100 that classifies lakes by their nutrient and productivity levels.
Eutrophic
A lake classification indicating high nutrient levels, reduced clarity, and frequent algae blooms, a nutrient-rich and highly productive lake.
Cyanobacteria
Photosynthetic bacteria (commonly called blue-green algae) that can form harmful blooms and produce toxins dangerous to humans and animals.
Algal Bloom
A rapid increase in algae population in a lake, often visible as green discoloration or surface scums, triggered by warm temperatures and excess nutrients.
Fish Consumption Advisory
Official guidance from state health departments recommending limits on eating fish from specific lakes due to mercury, PCBs, or other contaminants.
Source: EPA National Aquatic Resource Surveys, 2026.