Zooplankton are microscopic animals that consume algae and bacteria in the water column. Some types of zooplankton feed on algae, others on other zooplankton, and some take in both plant and animal particles. Larger zooplankton can exert significant grazing pressure on algal cells; however, they are also subject to predation as they are a food source for larger crustaceans, aquatic insects and fish.

Most freshwater zooplankton are part of only three phyla: Amphipods, which include both cladocerans and copepods; rotifers; and protozoa. Cladocerans and copepods are microscopic crustaceans that feed primarily on phytoplankton. These organisms can be an important food source for fish and can also exert grazing pressure on phytoplankton populations when present in high enough numbers. Rotifers are microscopic animals that feed on detritus and smaller organisms, such as bacteria. They can also serve as a food source for larger zooplankton. Protozoans are single-celled organisms that feed on other microorganisms, organic matter, and debris.

The zooplankton population in Cherry Creek Reservoir in WY 2021 was less diverse than the phytoplankton population with an average of 11 species, which is typical for a Colorado lake. Copepods were typically the zooplankton present in the highest numbers in Cherry Creek Reservoir and accounted for over 50% of the total population throughout the summer months.

Useful Links

• link Monitoring Report: Executive Summary Zooplankton
• link Section 4.15.2 Zooplankton
• link Colorado Parks and Wildlife Waterfleas Fact Sheet