Question

between 1920 and 2011, the number of species of mussels in michigans rivers went down. what is one reason this might have occured?

Explanation:

One possible reason could be habitat loss. Human - made changes like dam construction, river channelization, and pollution can destroy or degrade the mussels' natural habitat in rivers, leading to a decline in species numbers.

Answer:

Habitat loss due to human - made changes (such as dam construction, river channelization, and pollution)