You probably do not want to add the hyacinths to your swan's pond. Water hyacinths are an extremely invasive species and may overrun the habitat very quickly. We're not sure that the swans will eat the hyacinths, and these plants could overrun other plants that the swans may need in their diet.

We would suggest that you plant lemongrass, pickerel weed, duckweed, etc. Duckweed can also be invasive to the point that you can't get rid of it if there is no water flow.

Place a small fence around the new vegetation so that the swans cannot access the plants until the new growth takes hold. You will need to plant the vegetation not only in shallow water, but go about 6-7 feet deep. A swan's neck can reach approximately 4-5 feet. So, if you can establish the vegetation in a plot (12 x 24 feet), behind fencing, then, the plants should be able to get a foothold before the swans are able to yank them from the soil. Give it a couple of months to grow. In shallow areas, the swans will be able to grab the plants at the base and may pull them from the roots. However, at 6-7 feet, the birds will only be able to strip the top reeds/grass instead of the roots. Thus, the plants can still keep growing under the soil even if their reeds/stalks are eaten.

We hope this makes sense. In any case, the lemongrass and duck weed will be much more palatable for the swans than water hyacinth. Water lilies are also not very good because they have spike like structures under the water's surface which can possibly injure the swans' eyes or feet under the water and can also spread throughout the pond. We have seen swans in ponds with water lilies and the swans will not eat the pads. Additionally, water iris is poisonous, so it is extremely important that you choose aquatic vegetation carefully.

Swans will also eat torpedo grass (so they help keep the pond area clean and trimmed). You may want to plant rye grass and petunias around the habitat (use organic-no insecticides/pesticides, etc.) and allow the swans to graze on land while the sub aquatic vegetation is growing.

One last note, water hyacinths and lily pads that overtake a habitat are an inviting habitat for banded water snakes and water moccasins. We have seen water moccasins attempting to hide/nest under swan nests in overrun reed areas. One bite from this venomous snake can not only make the swan ill, but can kill them. Sometimes, a clean pond is much better for swans than having so much plant life that they may not be able to swim or invites unwanted wildlife. The Regal Swan