See if you have a supplier of bentonite clay in the area. Drain pond. Let dry somewhat. Put layer of bentonite down. Rototill lightly. Pack. Fill pond. The devil is in the details. How much bentonite?

Really a beautiful area now & with all that great help you have some precious memories along with the pump from your folks! The adopted kitty looks so at home in the wheelbarrel, same color as she! How nice that is near the porch so you can hear that great sound of running water. Cleaned out the shed a bit too so you can go to yard sales this summer & get some more goodies! Win ,win all around! Jan

Waterbug guy, First I will talk a little bit about concrete in water. You say it is a myth that concrete in water can kill fish and raise the PH. When concrete first sets up the surface PH is 12.0. Which is the same PH as a drain cleaner called "draino". As it is exposed to the CO2 in the air the PH goes down. But water is a very good leaching agent and so water will continue to try and get the chemicals out of the concrete. So will the PH in the water be raised? If the water has normal PH of 6.5 to 8.5 the answer is yes. The real question should be "how much will it raise it"? That question isn't easily answered as there are a lot of variables. Just to list some the age of the concrete, the condition of the concrete, is the water flowing over the concrete, the natural PH of the water, is the water being changed, and the volume of the water versus the contact area of the concrete. In some cases the rise might be so low as to make it very difficult to measure. But in other cases it can and does raise the PH to 9 to 9.5. At these levels it can and does kill fish. If I remember correctly you have stated that you are a pond contractor. If you are I hope you having started using roofing liner in the ponds that you build. Most of the time a person on this forum is never going to have a problem with roofing liner. Can there be a problem with roofing liner? This should be the question. The answer is yes. The chances that there could be a problem is very low. The largest pond product manufacturer in the US sent out a letter to all their customers a number of years ago. This letter said that all their liner in the future would be tested to be fish safe as they got a batch in that was not. In other words they were selling roofing liner as pond liner. This company had been selling a lot of liner for 10 years before this problem. If it had happen today with the wide use of the internet I would have think that some lawyer would have gotten this information and started a class action lawsuit against them and they would be out of business. The lawyer could easily have sued them not only for the cost of the liner that they had sold but for the cost to replace all those liners in the ponds built with them going back to the first time they sold this liner. The largest liner manufacturer in this country has told me that almost never would you ever have a problem with roofing liner but you might. I think that as a contractor you can't take that chance. If you were unlucky and did have a problem and were sued over that problem the lawyer handling the case would find out that they would sue for every customer that you have that has this liner. In other words you would be out of business. So is roofing liner toxic? No most of the time. But there is a small chance that there maybe a problem. I have only talked about 2 of the 8 things that you listed. I could easily talk about many of the other things listed but my point is this. You listed these things as black and white but they are not black and white. The only thing that is black and white about ponds is that all aquatic life will die. Mike

Thanks to folks commenting so far. Well, the area I want to clear up isn't too large, just a few feet wide going a few feet out. Perhaps about four feet to six feet wide going out three to four feet at max. So more like a couple dozen square feet rather than thousands, though the math is good to know. And I just want to clean it out enough to drop in a tiny floating dock again. The algae isn't too bad really, I think it's because the area is so overshadowed by the willow. Looks like most of the gunk is plant debris. Don't want to use chemicals- we have flourishing wildlife I don't want to risk with chemicals and I don't want to kill all the cattails, just clear out a thin spot of them. I think the original owners had this spot cleaned open a lot more than I'm planning on. You can tell it was cleaned out nicely at one time. And it really hasn't grown in much in the three years I've been living here. But I want to start tending this spot now before it gets any more grown in. Start maintaining it before dropping in the little dock. The little dock I'm planning on will be one barrel wide, about 3 feet. Probably using 12' long boards. Just enough to stick out into the water a little bit for one person to walk out onto. No boat launching or anything like that. More of a wildlife watching spot.