Just came across this article. Seems like chaeto can become a nuisance algae in waterways when not disposed of properly... microwaving it for 15s seems to kill it...
https://www.cambridge.org/core/jour...chaetomorpha/082901DC56D856BE3B4E03461C1D74FA
https://www.cambridge.org/core/jour...chaetomorpha/082901DC56D856BE3B4E03461C1D74FA