Question
How do I prevent cattails from taking over my natural ponds at a kids camp.  We have several and I have been warned that they might take over the ponds and kill off the fish?

Answer
Cattails are very prolific.  They are also hard to remove.  Even if you like to poison things (which I am against), few chemicals have much of an impact on cattails.  Physically removing them completely is nearly impossible but you can prune them.  Some animals like to eat cattails including ducks.  Cattails will not harm fish.  In fact, fry and small fish will hide among them.  

What the cattails can do over time is to result in the succession of the pond.  It's a natural process for a pond to become more shallow over time and fill in with all sorts of plant debris (not only cattails but leaves and other plants) eventually becoming land once again.  Obviously, you want the pond to retain depth in order to support fish and so on.  Depth is normally maintained in man-controlled ponds by dredging every 10 years or so which really harms the animals living in the pond at the time.  

Anyway, cattails are no more a worry for fish than other plants.  It's just that they grow much more rigourously.  They can be cut off manually to keep them under some control in smaller ponds.  I suggest contacting some of the companies listed on my farm ponds page for information on controlling cattails.  Unfortunately, they usually push poison when that's a bad idea for all the life that uses the pond.

http://www.fishpondinfo.com/farm.htm

Good luck!