Pruning overgrown Pickerel

I've got mature pickerel rush and lilly plants that have overgrown their
pots and rooted in the pebbles/whatever in the bottom of my 3 1/2' deep,
1300 gal pond. Anachris has grown around, over and through the plants.
It's a natural look, which has been healthy, fish are happy and looks ok.

But over winter the rush and lilly plants turn brown and probably need
to be pruned out and dead material removed so it doesn't rot and upset
the water balance.

Anyone find a tool or technique to prune out these dead branches? The
pond is too big to reach them from the edge and would be difficult to
climb into because of the steep sloping sides.

Ideas? Thanks!