This is a problem across ...

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This is a problem across Indian rivers.

As has been suggested by others Check for presence of toxic metals / other pollutants in Hyacinth. 

Hyacinth can also be anaerobically digested. I remember a plant being in operation in Sangali area in south maharashtra being operated on water hyacinth. I do not know the present status.

Composting is another option but check for pollutants.

However both above are for handling WH after their removal from river.

THere have been reports of  trials conducted by using insects and fishes who grow / feed on WH and which ultimately reduce the WH drastically.