If no fish I would nuke it with hydrated lime. It will tie up allot of the nutrients in less water soluble compounds. Rooted plants would have to then grow off it.

Dwarf sag is a great plant for ponds that fluctuate in water level. It can live out of the water and when the water returns will grow under the water. The crown or root will not die off but the green will dry and die then grow new. When the water returns it returns back to underwater life. I am working very hard on propagating this my self right now.

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7/8th of an acre, Perch only pond, Ontario, Canada.