Easy cover for small garden ponds

What are some easy, low-maintenance, preferably perennial plant and forget cover plants for small garden ponds?

I'd like to put in a couple small (4-6 ft diameter?) ponds in the 100'x50' garden area I'm planning at our new house. I don't know much about water features yet but have read you want about 75% of the surface area covered. I took a community workshop on water container gardening a couple weeks ago, and picked up a couple books at the library. Unfortunately the only things they talked about were tropical type plants that you have to maintain constantly and move indoors 5 months out of the year (I'm in Southern Ohio). The workshop instructor said those were about my only option.

Are there other things I can put in small ponds that won't be so much work? I just want a couple small water features to increase biodiversity, bring in beneficial predators and such.

Thanks.

it depends on your climate, but water lilies and duckweed might be options.

If you can find some, the small floating fern Azolla is way cool! It's a nitrogen fixer, and can multiply rapidly. It will run out of the phosphates in the water and then turn purple and slow it's growth, so plan on a phosphate source if you want to remove it for poultry feed or fertilizer....it's good for both. Volume for volume it's the equivalent of cowdung for soil nutrients, and has been part of the wet rice system in South and Southeast Asia for millennia (one of the few food-producing systems that has proven permanent, supporting high yields and populations without soil degradation)......Finding some near you and then getting it established are the main challenges