Since cattails are great wildlife habitat for birds and other critters, and are often a natural part of the pond ecosystem, I leave mine in, unless they are threatening to choke out the whole pond.
If you have the time/energy and don't want to tear up the pond bottom with a backhoe, you can cut off the plants at the base by hand using a sharp lineolum knife. Digging them out is really going to disturb the site.
There is one species of cattail (Typa angustifolia) that probably originated in Europe and is now considered invasive in the eastern U.S, but there is another common native species (Typha latifolia) that is a natural part of pond ecosystems. Lesser cattail, also called narrow-leaved cattail (T. angustifolia) has narrower leaves than common cattail (T. latifolia). Also, the male flowers of lesser cattail are separated from the female flowers by a section of stem. The flowering head of the lesser cattail tends to be much narrower than that of the common cattail.
Many land managers use the lineolum knife method to control the invasive one in wetlands that they want to keep free of it. The best time to cut plants is in the spring.
See the following:
TNC Global Invasive Species Team page
Invasive Plants of Ohio - Factsheet 11 - Narrow-leaved and Hybrid Cattail
Invasive Species -Common Cattail (Typha latifolia) - WDNR
I'm a biologist, and for me, I'd tend to leave the cattails in if they aren't covering too much of the pond. If they're really choking it out, they may be the invasive species. Maybe after you clean it up this time, you can keep after them with the linoleum knife method to keep them under control in the future.
-Matt