Yeah that's Quagga & Zebra Mussels usually...bad news:
https://cisr.ucr.edu/invasive-species/quagga-zebra-mussels
https://www.nps.gov/lake/learn/quagga-mussel.htm
https://www.watereducation.org/aquapedia-background/quagga-mussel
Yes, and Mussels thank you. :)