Water hyacinth is beautiful - and horribly invasive.

It is actually a "prohibited" plant in Florida, where conditions are nearly perfect for it to spread.

Conditions in TN probably won't be perfect, but should still be pretty good (to spread).

Water Hyacinth - Florida Advisory

You might consider starting it inside your pond in single Walmart plastic kiddie pool. Level a place on the bottom of the pond, drill some water circulation holes in the plastic, and put some good soil in the pool.

The water hyacinth should rapidly fill the pool. If you see any bit escape, I would drag the pool out of the pond and dig out every hyacinth shoot I could find in the rest of the pond.

If the water hyacinth behaves in the pool, then you could consider adding more pools and determining attractive ways to hide the rims in the pond.

In my non-expert opinion, there are many other rooted plants that will steal some of the nutrients from your algae, yet still not take over your pond and cause a NEW problem.

There are some good plant threads in the forum if you use the search function.

Good luck on your pond improvement project!