How To Stop Pond Pump Blocking Up My Pond Fountain Pump Keeps Get Blocked By Duckweed Stems, What Can I Do To Stop It?

My pond fountain pump keeps get blocked by duckweed stems, what can i do to stop it? - how to stop pond pump blocking up

There must be something more, because almost duckweek can dominate a pond and cutting oxygen supply. It's free and has no floating stems. see photo below
http://www.plantgeek.net/images/plantpic ...
You can see the river / creek photo below
http://www.flickr.com/photos/nilsa/53121 ...
Duckweed
None of the various small free-floating aquatic plants ,**** ***** Campion flower of the genus Lemna, more precisely, often carpet the colonies on the surface of calm water.
http://education.yahoo.com/reference/dic ...

Are you sure that this Frog? See Photos
http://www.cdfa.ca.gov/phpps/ipc/weedinf ...
http://www.flickr.com/photos/jennifersch ...
If ranula remove only a part.

Not recognize EDIT: The other answers that duckweed has no tribes.