Who’s In My Creek? Macroinvertebrates!

Conservation // March 18, 2021

When determining the health of a waterway, it’s the little things that count – literally!

One of the most reliable indicators of a healthy river or stream is its population of macroinvertebrates, the tiny creatures who live on the bottom of waterways. Though they don’t have a backbone (invertebrates), they are large enough to be seen with the naked eye (macro) and include thousands of species of crustaceans, mollusks, and aquatic insects. Beetles, caddisflies, stoneflies, mayflies, hellgrammites, dragonflies, true flies, and some moths, crayfish, freshwater clams, and snails are all common macroinvertebrates.

According to the Stroud Center for Water Quality, benthic macroinvertebrates are useful indicators for numerous reasons. They are common in most streams, rivers, and creeks, and fairly easy to sample and identify to get data – and while sensitive to pollution and changes in their habitats, macroinvertebrates have a relatively long life cycle and are indicators of water quality over a period of time. While scientists do use chemical water tests to measure water quality, they only show what’s in the water at the specific moment the sample is collected, and don’t give an indication of what was in the water in days or weeks before. Since macroinvertebrates are surrounded by water and any pollutants that may be in the water every day,  the quantity and diversity of macroinvertebrates present often provides a fuller picture of the quality of a river or stream.

What kind of macroinvertebrates are living in a given stream means a lot. Different types of macroinvertebrates have different requirements to survive. Some require cooler temperatures, relatively high dissolved oxygen levels or certain habitats. Other macroinvertebrates may be able to survive in less-than-ideal conditions — where there are low dissolved oxygen levels or more sediment — or where the water temperature is warmer. There really aren’t aren’t any “bad” macroinvertebrates, but the population present may indicate that there are bad stream conditions in which only the “strong” can survive.

Unfortunately, the Wissahickon Creek has poor scores on macroinvertebrate diversity, related to its largest water quality issue: stormwater management. Because of heavy development in the watershed, precipitation from storms cannot be absorbed naturally into the landscape and floods the creek, bringing road salt in winter and bacteria and chemicals during summer flooding. This harsh environment means that the creek can only sustain the most pollution-tolerant macroinvertebrates, like midges, water striders, beetle larvae, and snails. Find out more about what you can do to improve water quality in the Wissahickon Creek here.

Curious who’s living in the creek? Here are some great resources to learn more about macroinvertebrates:

  • Stroud Center for Water Quality: the center has resources and activities related to macroinvertebrates as well as other water quality issues.
  • Macroinvertebrates.org: a digital identification key for macros all over the Eastern United States.
  • TTF Watershed: our partners at the Tookany-Tacony-Frankford Watershed do extensive monitoring of macroinvertebrates in our area. Check out their social media on Macro Mondays during the spring to see up-close and personal finds!
  • PA DEP Index: a statewide database of macroinvertebrate observations in local waterways.