I remember the years when my water hyacinths use to multiply like that. Now I'm lucky if they multiply at all.
It's the gardener's life... you start to really think you know what you're doing and Mother Nature is like "Not.So.Fast".
@GBBUDD - we did have above average heat this summer, but the weird thing is it didn't FEEL like it. It just felt like... summer. I wonder if the average was pushed up by warmer nights. We had well spaced rainfall all summer which is always welcome. Things stayed really lush all summer long. Typically by mid-August we can quit mowing the lawn for a month to six weeks. Not this year. Maybe that's why it never felt overly hot - nothing looked like it was baked and crispy!
One thing I did notice when I was pulling my hyacinths out of the pond and pondless - the ones that were able actually get their roots into the substrate did waaaaay better than the ones that just free floated in the pond. I had to give them a good yank to get them out. Things tend to float right out of the pond so we have to put them in places where they will stay anchored, and this year those that were tucked behind rocks to hold them in place and in just a few inches of water did great and were the ones that bloomed for me. So my suggestion would be to put them where they can "touch bottom" and where they stay densely packed. (Now prepare next year for me to report that I couldn't even get the darn things to survive!)