Lake - what to do with it?

Hi all
I have a 4 hectare lake (10 acres). It is a man made lake, about 40 years old. It receives water from the local river, via a trout farm, then, it returns the water back to the same local river via what used to be a small hydroelectric plant.

It is all fallen into disrepair, and needs attention.

The turbine doesn't run, we were told the reason is that some metal grid fell into the pipe that lead the water from the lake to the turbine. The pipe is under water, so we have not seen it - to see it, we would need to lower the level of the lake. This we plant to do one day ...

The lake is very muddy. We don't know the exact nature of the mud. The shallower ends of the lake are overgrown with rushes, sedges, etc, and every year, they make new inroads into the lake - about a meter a year. If nothing is done, then one day there will not be any lake left... As the lake was also receiving the waste from the trout farm in the past, my guess would be that most mud would be of organic nature - in other words, plant and animal matter in different stage of disintegration. I think that the mud is less than a meter deep - mayeb a coupel of feet in some places, and in others less. We were told we would need to dredge the lake, but then, I read somewhere that it may be possible to deal with it differently: treating it with enzymes and lime and other things, which should "eat" the mud, and return it into a form usable by plants and other living organisms.

In the past also, we were told, there was fishing on the lake. It does seem to be an obvious source of potential income, but, we fear we would lose the lake to the fishermen that way. We fear that our lake would end up full of old hooks, and nylon, and whatnot, and it would not be safe for swimming any more. And to swim in it in the summer, with nobody around, just us, is simply magic.

My preference, my dream, is this:

Clear the lake off mud, and create what in effect would be a huge natural swimming pond. Plant it up with pants for filtering purposes, as well as for beauty. One or two little jetties, some nice accessible corners to get in and out, et voila! Plant the surrounding areas with trees and bushes that mirror in the water. I would like to open it to limited numbers of visitors who would appreciate swimming in nice surroundings, or simply watching it and relaxing next to the water. At some point during this work also repair the turbine, so we can have some free electricity as well.

Now, my questions...

1. how to determine the nature of the mud (organic? inorganic?)
2. what is the simplest and the most economical way of clearing the mud off the bottom of a lake - about half of which is shallow (less than 3 feet deep)

3. what is the best way to plant it up with filtrating and other plants - considering its size. In the swimming pond the plants would be planted in the gravel - but, the cost of getting so much gravel as to cover 2 hectares of lake is prohibitive. How to go about it instead? Plants in pots of gravel? Any other ideas? Does the swimming area need to be separated from regeneration area by walls? What would happen if they were not separated? (I see no particular problems there, but wonder if other people may see some other angles?)

4. what are the best plants to plant it up with so that the maintenance is minimal, but oxygenation, filtration and beauty are at their best?

5. how to prevent spreading of sedges and rushes another meter into the lake every year? Would digging of a ditch to make water too deep for them work? If not, why not? How to keep that ditch from filling up with mud in the future? What else may work instead?

I would appreciate your thoughts and ideas. Many thanks.
Happy work!
Warm regards,
Yves

Your mud is from two sources, one or both: topsoil or clay being eroded into the lake from the surrounding landscape and/or dissolved nutrients coming in, most likely from the trout farm, which encourage the growth of plants, algae, etc., which when they die and break down into a black organic mud.
Try to be sure that any runoff the lake is receiving is clean. Try to be sure that it's catchment is vegetated year-round.....if there is plow agriculture going on anywhere in the watershed, then there's a huge source of mud. Same with a dirt road or driveway. Another thing to try is to slow down and remediate the drainage from the trout farm before it enters the lake....perhaps by means of a small constructed wetland in there to physically get silt to drop out and nutrients to be taken up before the water enters the main lake.
Lakes do naturally fill in over time, so you will have an ongoing project to keep it from doing so, especially if it's shallow and getting regular doses of nutrients.
You might also think about turning the problems into solutions. Any mud you take out will probably be excellent planting soil. Perhaps you can replace some of the marginal vegetation with something more useful (wild rice? water chestnuts?) or beautiful (waterlilies, lotus....) There are also fish (grass carp) that will eat water plants, and others (carp, catfish) that will grub through the bottom mud for anything edible. Catching and eating these fish, and any others, will remove nutrients from the lake; although these scavenger fish will also muddy the water. For algae you really need a filter feeder, of which there are few of eating size in North America or Europe (not sure where you are) The Chinese grass carp is wonderful for this, but considered an invasive in many areas. But in general having a fully stocked ecosystem with plants (including submerged oxygenating plants and floating water-rooted plants), aquatic insects, fish, amphibians, etc. makes for clean water. Geese and ducks will munch marginal vegetation too, but they will muddy the water if they are overstocked....
Be thankful! I wish I had a ten acre lake to play with!

Hi Alder
Thank you for your post. I am thankful for the lake... I am based in France, and in France it is not impossible to find one to buy - even though I wasn't looking for lakes, this one came to me by itself. Kind of.

I would be interested to know if anybody had any experience in treating lakes for mud by means other than dredging. To dredge, we would need to empty the lake first, let it dry out, and then scoop the mud off the bottom. This is quite a complicated thing, as in France one is not allowed to drain lakes without many permissions, blessings by the officials, all based on studies written by experts etc etc, so I fear the whole party could cost a lot. That is why am looking for alternatives...

I like to thoughts to slow down and clear the water as it leaves the trout farm, and before it hits the lake. I am thinking about creating various water plant beds between the two bodies of water - which seems doable with a modest budget. There will be plants in the old trout farm as well, so that should all contribute to reducing the problem in the future.

Regards
Yves