Oligotrophic

Oligotrophic is an adjective used to describe the level of biological productivity of a waterbody. Many professionals classify levels of biological productivity using four trophic state categories: oligotrophic, mesotrophic, eutrophic, and hypereutrophic.

Of the four trophic state categories, the oligotrophic state is defined as having the lowest level of biological productivity. (The prefix oligo means "scant" or "lacking".)

An oligotrophic waterbody is capable of producing and supporting relatively small populations of living organisms (plants, fish, and wildlife). The low level of productivity in oligotrophic waterbodies is usually the result of low levels of limiting nutrients in the water, particularly nitrogen or phosphorus.

Oligotrophic waterbodies generally have the following characteristics:

Nutrients are typically in short supply, and aquatic macrophytes and algae are less abundant.
Oligotrophic waterbodies typically have less plant debris accumulated on the bottom over the years since aquatic macrophytes and algae are less abundant.
Oligotrophic waterbodies often tend to have water clarity greater than 13 feet due to low amounts of free-floating algae in the water column. The clarity may be decreased, however, by the presence of color (from dissolved substances), stirred-up bottom sediments, or stormwater runoff (particulate matter).
Fish and wildlife populations will generally be small because food and habitat are often limited. Oligotrophic waterbodies usually do not support abundant populations of sportfish such as large-mouth bass and bream, and it usually takes longer for individual fish to grow in size in oligotrophic waters. Fishing may be good initially if the number of anglers is small, but can deteriorate rapidly when fishing pressure increases and fish are removed from the waterbody.
A waterbody may have oligotrophic characteristics even though it has high nutrient levels. This can occur when a factor other than nutrients is limiting the growth of aquatic macrophytes and algae. For example, a significant amount of suspended sediments (stirred-up sediments or particles washed in from the watershed) or darkly colored water can retard macrophyte and algae growth by blocking sunlight.

Looks can be deceiving!
Because oligotrophic waterbodies typically have such clear water (Secchi depth readings greater than 13 feet) people often mistakenly think these waters are pure and healthy for human consumption. Unfortunately, human disease and death can be caused by bacteria, pathogens, and other toxic substances that are invisible to the naked eye. It should not be assumed that any surface water is safe to drink no matter how clear it looks. It should also be noted that in Florida, fish having some of the highest levels of mercury have been caught in oligotrophic waters.

See also:
Trophic states
Color
Limiting enviornmental factors
Limiting nutrient
Nutrients
Secchi depth
Total nitrogen
Total phosphorous
Water clarity

The information on this page was derived in part from the following publication of
Florida Lakewatch of the University of Florida Department of Fisheries and Aquatic Sciences.
This booklet may be downloaded in its entirety as a PDF file by clicking here.
Scroll down till you see the Circular 101 icon.

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A collaboration of the Center for Aquatic and Invasive Plants, University of Florida, and the Invasive Plant Management Section of the Florida Fish and Wildlife Conservation Commission.