Last year, I had very healthy and vigorous water hyacinths growing.

This year, my hyacinth roots have been covered with a dark green/dark yellow crap substance -- as a result, my hyacinths have been very sickly and puny.

What is this stuff on the roots? live algae? dead algae? (I'm not referring to the little bright green rice-like plants. I'm referring to the dark green stuff clinging to the roots)