Mussel & Macroinvertebrate Monitoring

Mussels and macroinvertebrates serve as excellent indicators of water quality and ecosystem health. These organisms provide critical information about the condition of a river or stream and can help guide conservation and restoration efforts.

Unlike other parameters, which provide a data snapshot in time, macroinvertebrates reflect cumulative environmental conditions over weeks or months or years, and the presence or absence of different species can quickly reveal problems or opportunities!

Freshwater mussels are fascinating aquatic creatures that can tell us detailed information about the long-term health of waterways and aquatic ecosystems. Mussels are often considered to be “canaries in the coal mine” as they are very sensitive to different pollutants.

Twenty-eight of the 51 mussels in the state are listed as threatened, endangered, special concern, or species of greatest conservation need, or species with informational needs.

Why Do We Monitor for Macros and Mussels?

Macroinvertebrates and mussels have varying levels of tolerance to pollution.The presence of pollution-sensitive species, like mayflies and stoneflies, indicates clean water, while pollution-tolerant species, like leeches and midges, suggest poor water quality.

Often overlooked, native mussels actually purify the water they live in – filtering as much as 10 gallons a day per mussel. Mussels are a great indicator of a river’s health which can be evaluated by surveying how many and what types of mussels occur within a stream reach. Mussels come in many varieties of colors, shapes, and sizes, and depend on fish as part of their reproductive cycle. Milwaukee Riverkeeper surveys mussels as part of a larger effort by the Wisconsin Department of Natural Resources Mussel Monitoring Program, which is looking to gain a statewide perspective on mussel populations.

What Can We Learn from Mussels?

Threats to mussels exist from sedimentation and runoff from both agricultural and urban sources. Mussels are particularly sensitive to stormwater runoff when combined with treated wastewater, due to the combination of heavy metals, ammonia, and chlorides. Mussels can live 40 years or more; however, young mussels in particular are sensitive and do not survive the presence of these contaminants. The data collected on mussel populations provides insight into water quality and long-term health trends that shape conservation efforts for the Milwaukee River Basin.

What is a Biotic Index?

A biotic index is a scientific tool used to assess the health of a water body (like a river, stream, or lake) based on the types and abundance of macroinvertebrates. It provides an indirect measure of water quality by examining the tolerance levels of organisms to pollution or environmental stressors.

Scientists or volunteers collect and identify the types of organisms present in a water sample. Each organism is assigned a pollution tolerance score. The biotic index calculates an overall score based on the tolerance levels of the collected organisms. This score gives an indication of water quality:

• Low scores: Poor water quality (dominated by pollution-tolerant species).
• High scores: Good water quality (rich in pollution-sensitive species).