Azolla, Salvinia, and duckweed (lemna species) can get out of control in a hurry, but if you have a small enough water feature it should be easy to scoop a bunch out with a net and toss it out. Duckweed is the worst because it is so small and gets everywhere. Keep on top of them and you should be ok. Bright light grows these faster, lower light slower. Azolla colors up reddish in higher light as well.
Another good floating plant is Pistia stratiotes (water lettuce). It grows fast when it likes the conditions, but it's easy to control by removing offshoots or larger plants, whichever you prefer. The roots do hang down quite a distance though. Bright light grows it fast, lower light keeps it alive.
And one more amphibious plant is Hemianthus callitrichoides. It can grow submersed, emergent, or emersed. Bright light is required to grow it well, otherwise it is weak, leggy and straggly.