My 1.75 ac pond had a lot of watershield in all areas under 6' in depth. By summer it would be impossible to fish from the bank. Normal water visability is about 3-4' except when the weeds die in fall and I get a bloom - then the visability drops to about 2'.

As noted in other threads I treated one bank with Navigate herbicide and it pretty much killed all weeds on the bank treated and about 95% of the weeds in rest of the pond. I found I could get a bloom when fertalizing the few weeks after most of the weed died.

Now some of the weeds have grown back - about 15% of what it had before but enough so I can't get a bloom fertalizing. It seems like a losing fight to try to keep pond in bloom so I am leaning towards keeping about 30% or shoreline clear and just letting weeds grow elsewhere as the weeds seem to provide a lot of habitat for the small fish. I am feeding about 10lbs of fishfood each day - I can over feed without too much worry.

I'm curious if there has been any studies of how much weeds like watershield provide in the way of fish nutrition vs. a bloom?

I would try imazapyr on the water shield. Very rarely have I seen regrowth in the same year after using imazapyr. I've had mixed results with navigate but some people swear by it. It doesn't seem to have as long lasting of a kill though. Your water Alkalinity will drastically impact how well your pond holds a bloom, low alkalinity ponds don't tend to hold a bloom for more than a couple of weeks. Water shield isn't going to provide nutrients for your fish, but it will suck up the fertilizer you intended for a plankton bloom.

I wouldn't expect plants to provide nutrients but they do seem to provide a home for many small creatures the fish eat.

I used a imazapr based herbicide this week on the bank I want to keep clear. Not sure it will have the desired effect as it rained within 15 hours of application and water levels have risen to extreme heights washing it off. Have noticed a few of the weeds turned yellow so it had some effect. The Navigate pretty much killed all the weeds systematially - I believe if I had spead it on all the banks it would have took them all out.