pond weeds

I need some advice on pond weeds. Our largely spring-fed pond, built
about 40 years ago, is about 3/4 surface acre and 15-17 feet deep in
the middle. Edges slope so there are reeds & cattails, not such a
problem as I guess they cannot grow in more than 3-4' depth. The
problem is a weed which a Dept of Lands ranger called duckweed. I am
not sure that is what it is since picture on the Web look a lot
different. Our weed leaves are enormous to those I've seen in
pictures.

This weed growth has really increased in the last 5 or 6 years as
there is some drainage into the pond from higher up on the hill where
people are building homes on 5 acres lots is probably from fertilizer
use on lawns, etc. We cannot prevent this influx.

The weed leaves are 2 or so inches long, like a fat spear shape.
Stems are vining and rooted in - they seem to reach clear to the
bottom. There is a seed-head looking thing here and there on the
stems, and is 2 or so inches long, narrow. The stems look for all the
world like philodendron gone aquatic.

Strangely, the bass, frogs & other creatures in the pond are having a
wonderful time and have no problem with this canopy of leaves.

My husband spent the last 2 days in a boat hand "weeding", hauling up
miles of stems and weeds so we can set up a water line from the pond
to our garden. We have to clear this or the leaves will clog the
water line filter. It was discourage as he barely made a dent the
stuff is so thick. He cleared a lot last year and of course, it grew
right back.

Hopefully, you can see the pictures of it at Shutterfly link below:
http://share.shutterfly.com/action/w...2bMXGw&notag=1
Just click on view pictures, then choose slide show - no need for a
password.

Does anyone know what this is and how to get rid of it, or at the
least, reduce it so it doesn't choke the pond to death plus make it
impossible for us to use our water line.

Thank,s
Deb