Howdy folks. We’ve got several ponds on our place with good fishing. We’re in east texas and build our ponds and dam out of good RED clay.

I want to build a pond specifically for swimming and fun stuff and I want to see how clear I can possibly make it.
I don’t want to spend the money on a liner.

I have all the equipment a dump truck and the experience, I’ve been building them for a long time.
I don’t care if there are fish in this pond at all, the main goal is clarity, but at the end of the day the only material we have is red clay.

I thought about building it like normal then adding copious amounts of hydrated lime and alum?
Or even trucking in crushed white rock driveway material and lining it with that.
I’m open to any ‘outside the box’ ideas. Like I said clarity and obviously swimming safety is the main goal.
Any thoughtS?
Thanks in advance
Ethan Tremblay

Think about weed growth due to clarity. This may or may not be an issue, depending on how you view weeds, but it does need to be considered.

Consider a shallow area full of plants to help "purify" the water like they do for "natural" pools. https://pondmegastore.com/pages/beautiful-planting-ideas-for-natural-swimming-pools

You will probably want SOME fish to consume insects growing in/falling on the pond. Swimmer friendly species include Fathead Minnows and Redear Sunfish.

I agree with RAH. I don't think you can turn a pond into a "swimming pool" without some kind of system to control algae.

City pools use lots of chlorine. I think the best pond option is to use plants to take up the nutrients, and essentially starve the algae.

Here is a link that gives more background on the theory of natural "swimming pools".

Natural Swimming Pools

I also agree with Theo, that some fish will make your pond better. If legal in Texas, I would definitely consider stocking gambusia (mosquito fish).

Typing my post made me think about possible beneficial fish for Ethan's situation.

Has anyone on the forum tried that kind of pond with a few tilapia for algae control? If they clean out the algae, do they start on your filtering plants?

Has anyone tried threadfin shad? I think having a pelagic filter feeder would help clean up the water column. If the TFS eat most of the plankton and clarify the water column to the bottom of the pond, would that make the algae and rooted plants (in unwanted areas) problems worse?

Ethan, are you in NE Texas or SE Texas? If in NE, then tilapia would probably die every winter so you could easily control your population after you determine the optimum number. Likewise, the TFS would probably die off during cold winters, depending on your exact location and pond depth.

There is a place south of us where scuba students take tests. It was some kind of a quarry for white driveway rock.
It’s super clear a very beautiful but the water chemistry makes it pretty much sterile, there’s no fish or plants in it. I was thinking of trying to replicate it without actually having a quary.

https://www.tripstodiscover.com/blue-lagoon-in-texas/

The Blue Lagoon has several advantages that will be difficult to replicate.

One is the steep sides (in most places) and the deep bottom (28'+) that is below the photic zone (where sunlight can reach). That stops much of the plant growth and also suppresses the origination sites for the growth of filamentous algae. There are some rooted plants in the shallow water around the shoreline that is not a sheer cliff. Those plants do take up some of the nutrients from the water column.

The Blue Lagoon is also spring fed, so there is no input of nutrient-rich surface runoff. What will be the water source for your pond?

Is your red clay already densely packed in place? If so, then you might be able to excavate a "tank" with vertical sides and a deep bottom. Obviously, you would need a dock with a ladder for ingress/egress. However, such a pond would be dangerous if any non-swimmer ever fell in.

You can also use the pond dyes to further inhibit the growth of photosynthesizing organisms.

Finally, there are some really powerful herbicides and algaecides available. If you are contemplating zero fish, then you might be able to heavily dose your pond between family events (as needed).

I believe phosphorus is usually the limiting nutrient in most ponds. I am pretty sure a few people on the forum have even tried some of the phosphorus reduction or sequestering processes to lower the productivity of their ponds.

I am not sure you can make your pond sterile like the Blue Lagoon with just the addition of lots of limestone gravel. I believe the biggest reason it is "sterile" is that it is only fed with spring water.

Hopefully you can get some of the chemistry experts to add some advice to your post.

In both ponds, you will get nutrients coming into the pond via air and wind. Dust, pollen, leaves, etc. The reason (I believe) that the Blue Lagoon is so clear is the volume of water in relationship to the surface area. Plus what FishinRod said about the depth. Tilapia will help control the filamentous algae, but even so I bet you will see a phytoplankton bloom due to nutrients in the air and soil entering the pond. LOTS of plants will get the water crystal clear, but since they can grow down as far as sunlight will go, that may become a problem as they grow year after year. Chara doesn't grow tall, so that is another option.

Thanks for the advice! You guys really know your stuff!

To be clear(no pun intended) I’m not opposed to fish, or being sterile/not sterile. I only stated that to let you know I would gladly sacrifice fish for clarity. If there was a chemical that made it clear but killed fish I’d be ok with it.

Most ponds we dig are located in a runoff terrain to maximize watershed area. This pond I was thinking of building in such a way that runoff would not enter the pond at all. I have a good spring and a solar pump I can use to pump spring water directly into it.

I have a friend in the Houston area who built on a few years ago and lined it with stabilized sand (10:1) mixture of sand and Portland concrete. His worked pretty well but we don’t have any local sources for it and the truck would make in too expensive.

The soils that line my pond are pulverized dolomite, which is basically limestone. This has lead to a nutrient poor pond, resulting in some fairly clear water and an excellent swimming pond. When we haven't had runoff in a while, the water does take on that blue-green characteristic of hard/alkaline water and can see at least 8' down. We do get plant growth, thanks to curly-leafed pond weed, but isn't too bad after 10 years of pond age, we still haven't needed plant management.

Key points:
1. Crushed limestone lining may free up enough hardness/alkalinity in the water column to make phosphorous less effective, and water conditions less hospitable to some plants. Note the FA is a rarity in my pond. You probably need a fairly thick layer of materials of a variety of sizes so it doesn't get locked away under sediments easily.
2. Consider parts of the pond non-swimming areas to let transitional plants grow intentionally. Especially on sides where runoff enters the pond. It will slow water flow to reduce turbidity, and catch debris before it enters the swimming area. I have buffers of cattails and pond lilies on the upslope side from where all my runoff comes from. Both of these plants will capture excess nutrients from the bottom decaying materials and lock them up. They don't really pull from the water column directly.
3. Chara will come naturally, and makes an excellent "skunk bomb" for kids to throw at each other. It does grow very well in alkaline waters. Part of the reason I don't have much FA is chara out-competes it.
4. Alum treatments when limestone isn't doing the job entirely.
5. As suggested, you will want fish. No bluegills, they are jerks. I have yellow perch, black crappy, and walleye in my cold waters, and you don't see them swimming unless you stay very still. The one lone bluegill will track you down and bite you out of spite.
6. Keep pond construction as far away as possible from trees and anything else that would put nutrients in the pond.

Bluegills in a swim pond are like Henery Hawk - not big enough to do any real damage, not smart enough to pick on somebody their own size,
but plenty enough obnoxious to keep all the other critters in the barnyard in a constant state of warfare.

Do you have enough area to dig another pond that is roughly the same size (surface area) of the pond but only deep enough to keep 3'-4' of water all year 'round? If so, fill that shallow one with submerged plants and then pump water from the swimming pond into it and let the water go out of it on the other side of the inlet - push the water the length of the pond so the plants utilize the nutrients but aren't becoming a problem in the swimming pond.

Ethan, fish eat mosquito larvae. Without fish…..