You can pull them by hand or cut them just below the water surface.
When using that method, make cut in mid to late summer (July or later), cutting them in May will stimulate their growth because they are already using most of their energy for spring growth. Repeat the cutting two or three times, and each year you should see fewer cattails returning. If you want to remove them completely, remove the entire root.
In some places it is illegal, so I would call my county extension agent for advice.
Hi Marianne: You can cutthe cattails off 2-3 inches under the water line. Once the cattails are cut, the oxygen to the root system is cut off and the plant will drown. But, keep in mind that Cattails can be desirable in a pond. They provide important wildlife habitat, shelter for birds, food and cover for fish and for the insects they eat. Cattails help protect the banks of a pond from erosion.
Here is a site that gives some information on getting rid of them, but you have to arrow over several times to get to that part, but it's helpful:)