I ditto tiller and others. Good advice from all so far. The only thing I would add about chemicals...is that there is one bottle of stuff you really should have, and that is a water treatment for Chlorine and Chlorimines. Chlorine is not that bad if you add less than 10-20% of your total amount at once. The fish can get Gill Burn if they play in the hose spray so put the hose in a area they can't get to. The chlorine will hurt your bacteria colonies in your bio filter but won't wipe em out. After a day or two contact with the air will dissipate the chlorine (it will go faster if you have an airator or waterfall). Chlorimines though are baaaad. They will never leave your pond without being treated with an additive. You can call your water company and see if they use chlorimines. If they do, then you need to get in the habit of using a neutralizer every water change. If they don't then you can get away without, unless you notice your plants being hurt by chlorine when you change the water. "Bad stuff" on the bottom are organic compounds like leaves, fish poop, dead fish etc. As it decomposes it will create a layer of mud called "muck". It's black and smells bad. If your pond ever has a sewer odor that's a sure sign that your muck has run amok and the fish are in danger. When this happens oxygen levels drop and you start getting brown algae and your water will look like rootbeer. Anaerobic bacteria start to go to work in the oxygen free environment. This is a fish death sentence. You should regularly scoop out the majority of the muck leaving as little as possible on the bottom after it settles back down. "Regularly" depends on your pond. More trees, dust, pollen, weaker filter etc mean you need to clean it up more or less than others. There is no rule about how often to clean. To clean out muck, you just need to scoop it out. You can do that by hand, with a bucket or shop vac. One thing I like is this little attachment that goes on the end of a garden hose. The flow of the hose water creates venturi suction that pushes the muck into a little nylon bag. Keep in mind that with any of these options you will stir up the muck and it will take a day or so to see improvement. If you do it regularly, the stirred up muck isn't a problem for the fish. But if you have a deep layer of it you might want to do what destany said above, and move the fish into a container for a bit (filled with pond water!) as all those bad compounds will be spiked during the clean. If your depth is closer to 3 feet I would still think about either getting rid of the goldfish (donate them to a pet store or other ponder) or the koi. With either 3 koi or 11 goldfish you have about the right fishload. But with both, you have about double what you will need in a year or so when they get big. If you are dead set on keeping all of them, you need to plan on losing some to stress or plan on getting a heavy duty biofilter and/or doing regular muck sweeping.

It isn't just the heat, 7% humidity I think is even worse. For a few years I've been experimenting with marginals and other plants growth in a water tight container. I've been trying to learn what works where. Cannas, Iris and tomato all slowly go down hill through summer in full sun. Pretty ugly, but alive. Much better if shaded part of the day. Too much shade and growth isn't good, few if any blooms. In a perfect world shade could be added in summer and full sun the rest of the year. Tomato was pretty worthless though. Along the line of Egyptian papyrus I've found Umbrella Palm (maybe Cyperus alternifolius or Cyperus involucratus, not sure) did super all summer in full sun. I got it out of a neighbor's yard. A surprising number of marginals are grown here in yards. Many marginals are adapted to store water for lean periods. Following that line I've been using nut sedge with very good results. Bright green, full when planted in mass, all summer full sun. It's a mondograss look alike. I'm trying mint right now and so far so good. Giant Reed, Arundo donax does great. Here some strangeness...I've been growing a several Chilean mesquite trees from seed in 5 gal buckets, clay soil, no drainage. These are watered everyday, but not to the point of standing surface water. When I've removed one from a pot there were roots down to the bottom of the bucket in standing water. Long term I assume some bacteria is going to get the upper hand, but it's been over a year and so far they're doing very well. Same for a few Fan Palms. Elephant's Food, Portulacaria afra doing well in no drainage. And it can be Bonsai. Pencil cactus, Euphorbia tirucalli, (not a real cactus) has done well no drainage. I would try any plant. Cactus is on my todo list. As McKool said, crown above water level for marginals is best, but really true for these non-marginals. And I can't expect these are always going to do great, rot is an issue. But if I can get some good years out of them I'm going for it. Gardening here is like being on another planet. I threw away my Sunset Western Gardener book which I relied on in San Jose CA.

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.

LOL, chas. You are correct, the initials do stand for Dept. of Natural Resources. As can be expected there are a lot of those alphabet agencies out there that may or may not be helpful. Which one has helpful info. in your area varies in the extreme. Some are identical to other agencies that have totally different objectives. Then there are private companies that want to sell you something. Mokitty, there is no reason in the world why a holding pond, retention pond, dew pond cannot be ornamental. From what I see in the photos, someone has tried to do that in the past and has recently let it go. Recently being totally subjective. The grasses around the pond can be cut back, the old bridge removed or replaced, wild shrubs and other plants identified and volunteer saplings removed. That should keep you busy for a while. Cutting back the grasses will help control the number of migratory ducks that use the pond.I wouldn't mention the ducks to anyone but the Extention service and would be cautious even there. They might prevent you from doing anything that might change the current function of the pond including cutting the grass. The Environmental Protection Agency is well known for that. Avoid them if possible. Here are some sites that look like they can give you decent info on the purpose of your pond. http://www.gotalgae.com/retention_ponds.htm coastalwaterwatch.com/product2121.htm http://www.co.monmouth.nj.us/documents/61/Stormwater%20Management%20Basins.pdf Call the DNR and the Extension service and specifically ask "Do you have any material related to small retention ponds or dewponds and wildlife habitat?" This is one of those projects that may or may not require lots of planning and/or physical intervention. For now, look for traces of a previous pathway to the pond and improve that. Starting at the bridge may go faster. Observe what the weather does to the water level. Keep track of water levels for as long as you can, months are better than weeks and compare them with rainfall. See what happens to the pond and the surrounding area during and after a heavy/light rain. Locate and clear any over/outflow. Identify grasses and other plants. They may have been chosen for specific purposes such as erosion control, wildlife cover, food source, etc. Tall grasses may prevent debris from overwhelming the pond. Search for electric hookups. Do they even exist? Is there a bad odor like sewage that would indicate dredging for organic matter is needed and the pond is deficient in oxygen. Float something on the surface to see if there is any sort of water movement. You might find that overflow where your float ends up. Check the soil on the outside of the pond and on the inside of the pond to see if it is the same. Are there lots of rocks on the sides of the pond? How deep is the mulm/debris on the bottom? Did the former owners leave any pond equipment behind? Get the water tested or get a testing kit and do it yourself. No strips. They just don't give good readings. There are people out there who can do the hard work of cleaning out the pond for a hefty price. Before you hire them, know enough about what the pond does that it will be you in charge. Ask questions. There are enough posters here to answer most questions or who will send you where you can get the right answers. I hope this has not overwhelmed you.