Raising the bottom of my ponds

I have a situation on my property that I haven't seen covered exactly in
these forums and wonder if anyone has any ideas. I bought my house ten
years ago and in the backyard are two ponds continuously fed by a stream.
These ponds were created by the original builder of this house by putting a
concrete dam on the original stream and having the created pond behind it
pour as a waterfall over a built-in lip in the middle of the dam to a lower
pond which contains a square drain towards the other end of it which drains
the excess water to a continuation of the original stream in a pipe under my
neighbor's driveway. The problem is silt/sludge. There's a LOT of it built
up over time and I'm very concerned about safety at this point with two
little girls of my own and a dam that seems to attract every kid in the
neighborhood. The mud/sludge buildup especially in the upper pond is
dangerous - it reminds me quite a bit of quicksand and I shudder to think
how deep it might be in the middle. What I would like to do is:

1. Dredge up this muck - at a minimum, it would drastically improve the
appearance of the ponds, especially the upper one which now has weeds
growing from this stuff everywhere. I also have shoveled some of this mud
up from the edges and used it in places where I wanted to plant some grass
and it is *spectacular* as top soil for this purpose. Would a standard
trash pump be up to this chore? I don't need to do this in a gigantic rush,
but I would like to get started on it and keep at it, and a regular 3" trash
pump is quite affordable if this is the right choice.

2. Raise the deep parts of the pond up to safe levels - I don't want the
middle of either of these ponds to be deeper than 2 1/2 - 3 feet. I'm not
sure how deep either one is at this point but would need to fill it in with
something appropriate (and sturdy to walk on if desired) and possibly top
that off with some nice round river stones. What would be the best material
for that? Clay? Fill? Once this project was somehow achieved, I'd
obviously want to keep these ponds as clean as I could after and wouldn't
want to inadvertently suck up fill or whatever during cleanings.

Any ideas on this? I can attempt to upload some pix of this to the NG if
it'll help clarify what I'm trying to do. Thanks in advance.

Mike O'Connor