Hi Heather:
The pond's primary problem is the runoff from adjacent fields into the pond.
That will bring in phosphates, nitrates, etc from fertilization of the
adjacent lands which will feed the algae, resulting in uncontrolled blooms.
Barley straw, plants, UV, etc won't even to begin to eliminate that kind of
algal problem, until the source of ground water containing
nitrates/phosphates is controlled.
You really need to rework the ponds sides, to build a berm to prevent inflow
of ground water from those fields.
Of course you may need a little flow to keep the pond's level up, if your
pond doesn't have springs feeding it.
Good farm ponds are not setup to fill by flows of water over their sides
from adjacent terrain.
Also streams should not be allowed to flow through ponds, or you will have
silt issues, just as you are describing.
It is not that difficult to hire a contractor to pump down the water level,
even on a 4 acre pond, and rework the sides.
Happy ponding,
Greg


"Heather" wrote in message
...
If there is anyone here with large recreational pond experience could you
please comment on clearing algae?

The pond in question is 3 - 4 acres and 30' at the deepest. It has some
springs. The bottom is limestone and silt. Lotsa silt. The sides slope
so
adjacent runoff goes into the pond. A field is nearby and during severe
thunderstorms there is a "river" running off the field and into the pond.

I suspect that the nitrate level is high. (Think I'll take my fish pond
testers and check the levels to see.)

Also there is little plant life. Some weeds along the east shore. Some
fish, bass, pike, sunfish etc.

The owners have asked me what they should do to clear the algae since this
is used for recreational swimming and SCUBA diving.

If I advise them to plant hardy water lily will this help? Water hyacinth
would be expensive for so large an area and in Zone 5b.

Anyone ever rig a homemade UV filter using 4' black lights protected by
glass or something like that to use on a large pond?

Thanks for all help.

Heather