My sprinkler system did a strange thing. Sprinkler draws from a lake,
stopped working about 1 month ago, (house is cira '85), I replaced the
intake pipe, the screen head, and the back flow valve. Pipe extends
out about 20' and floats (attached to a duck float). All went well
and the sprinkler was working fine for about 3 weeks. Then I notices
a slow reduction in the amount of water coming out, unitl finally no
more. I check all new connections, all is fine. Pulled the pump
apart, impeller looks good, a couple of gaskets warped but nothing
terrible. (intake head has screens to prevent unwanted items entering
system)

Any ideas???