I like to leave some weeds emerging from the water in certain areas. Wild ducks are attracted to it and like to forage in the weedy areas, as it provides habitat for various critters.
Weeds in the shallows also give dragonflies a place to breed, as well as a place for the resulting dragonfly nymphs to climb out of the water and complete their metamorphosis before flying off to prey on mosquitoes and flies and whatnot.
