What type of floating plants can I use for a half acre pond for fish cover
Want something that will not take over

All living plants are going to spread; some faster than others. How deep is the pond and how much of the water surface is less than 6' deep? Many of the hybrid water lilies will grow to 4' and many to 6' deep.

By plant cover, I presume you mean shade for fish and some protection from predators? The hardy waterlilies will do the job though you would need to crop them maybe every three or four years.

A hardy lily might put on three or four feet growth a year, at least they wont be invasive and tunnel uncontrollably into a lake bed like cat tails or lotus might.

A few good names to look for among the hardies , gladstonia, attraction, rembrandt, colorado, hollandia, pink sensation, sunrise are a few.

Try not to be tempted by the 'cheapo's' that are often thrown in a pond, its not a bad idea to put varieties in with good blooming characteristics as when you have a surplus, you will find the good ones fetch a reasonable price on e-bay, whereas plug plain whites like alba or a pink like carnea are less easy to get rid of



Regards, Andy