Trying to Understand Natural Pools

I want to build a swimming pool on my lot and would like to build a natural pool.  I've been reading up and searching for information on the web, but it's hard to get good details.  I finally bought a few books (and they're all expensive - hard to find ones that aren't!) and I've been reading a few things that make it seem like a natural pool is a bigger problem than a conventional pool.

I've found very few forums where natural pools are even discussed and it seems like there are people here who have built natural pools, so I hope I can get some answers here that will help me understand natural pool issues.

We have a large wooded lot with a barn about 300' behind the house.  (Old cinder block barn - it'll be a recreation area and guest house when it's renovated and fixed up.)  Near that old barn is a lagoon that was a cesspool at one point.  It's about 170' long and 25-40' wide (it's hard to measure the width without trudging through it holding a measuring tape).  I've talked with a number of people about the issues of this having been a pig farm about 30 years ago and have had many people, such as environmental quality people, environmental engineers, and more, tell me that, at this point, any yucky stuff has biodegraded 20 or so years ago.  Aslo, I know the previous owner dredged out this lagoon to clean out any waste and gross things in it.

My original idea, before I started research, was to drain the lagoon (it's not filled more than about 8-12" anyway), clean it out, and use it as a the plant and filtration area for a pool and to dig a separate spot nearby for the actual swimming area.  That leads to the first question: Does the filtration area have to have a liner?  I've seen a few "how to" directions that indicate it does.

And that question leads to a lot of my other questions.  The area where the pool will go is wooded.  Whether it's a conventional pool or a natural pool, I know I'm going to be cleaning leaves out of it.  (There's no way I'm cutting down any trees I don't have to cut down!)

The more I read about natural pools, the more it sounds like they have to be as carefully isolated from the environment as a conventional pool.  One book warns me to keep waterfowl out and prevent them from being able to poop in it.  I can enclose the swimming area, but not the filtration area.  I've read, in several places, comments about the need to prevent animal access to the entire water system of a natural pool.  For instance, keep deer out, foxes, raccoons, bear, and anything else.  And, above all, make sure wild animals don't pee or poop anywhere in the pool water system.

Along with reading about issues like that in "how to" books and websites, it turns out that in the few places I could ask anyone about natural pools, I always get comments about diseases someone can get in one.  (I've spent a large part of my life swimming in lakes, large creeks, and rivers - I figure the thread of something like Naegleria fowleri (the brain eating amoeba) is not going to be worse in a cared for pond than in most rivers and lakes.)

I'd love to have a natural pool, but the more I read up on them, the more it sounds like they're basically "separated from nature" pools, even as much as your basic, old fashioned, conventional, chlorinated pools.  But what I'm reading makes it sound like it's a serious problem if a bird flies overhead and poops in the pool or filtration and plant area.

Could someone clarify this for me?  How isolated does a natural pool have to be?  Do I need to line the filtration/plant area for reasons other than to keep water in it?  (There is a layer of clay under the soil and drainage into the soil doesn't seem to be an issue.)  How important is it to make sure no animal waste at all ends up in the water?

I would normally chalk up a lot of the comments I've read to paranoia and to people who don't like a new idea, but when I read comments in books on making natural pools that make me worry about having to keep waterfowl out of the pool (which we all know isn't always possible), I can't help but to wonder just how isolated a natural pool has to be from nature and the environment.

This year I've been helping to build one at my friends place. It's basicly a Butler pool, 25 meter by 18 meter, two third regeneration zone and one third swimming area 8 by 4 meter. It didn't fill up completely with roofwater, because there has been very little rain. The deeper bit is filled up and air pumps are in place. It's chrystal clear with just a few plants in place. They swam in it every day in summer. Me too, that water is so much nicer than a chlorinated pool! Frogs live in there, swallows skim the water and drink. Insects swim around. It's not isolated from nature at all.
I have a very complex book about natural swimming pools which i wrestled myself through, but am very happy we followed the Butler method. It's cheap, easy to build , low in electricity cost and friendly to the animals in the pool. Although i think it's not an environmentally friendly thing to build a pool in itself, a lot of cement went in and artificial protection material for the EPDM liner, but the biological niche created is priceless. He had to have 25 cubic meter water for the fire brigade to get a building permit.
He's got all these you tube vids which show a lot, like him drinking his pool water after lab tests results have proven it to be drinkable, which i would not recommend,but the do not (surprise,surprise) show all, and you can buy a video with details of him. My friend has had contact with him when something wasn't clear to us. When it's full and planted in spring i will post a photo gallery on here. With the progress of course.
I have a small pond myself since a few years and it's filled with plants i gathered on canoe trips from around where i live which flourish and multiply, which i am going to transplant into his natural swimming pool.
Have a look at Butler's channel.
https://www.youtube.com/user/davidpaganbutler/videos

I dug and lined three koi pond in the old yard. The secret to keeping clean water is to dig your pond at least 12 inches deeper than you intend for the bottom of the pond. Then add sand to about 6 inches.

As time progresses poo and leaves and twigs will sink down to the bottom of the pool where anaerobic bacteria will start the ammonia cycle (the removal of ammonia from the water if you have frogs/fish/etc.

Ponds under trees fill with debris faster. You might want to lay paving stone over the sand. As the debris deteriorates it will become a slightly slimy thick liquid that will grow into the sand. You want to keep that as it is bacteria that is beneficial and it will eat the poo of passing birds.

I would assume that you would need a deeper pond, more sand and lots more debris to handle bathing cattle. Most of the 'natural' ponds that were dug by humans tend to be clay bottomed and slowly fill up with a black nutrient muck. It feels icky, but basically isn't that harmful.

To me a natural pool falls somewhere between aquaponics and regular pond for fish/irrigation that someone has build.
* Unless spring-fed make it super watertight aka a pond liner/cement/etc
* growing area at least = volume of fishpond/swimming area
* Get algae eaters to keep it looking clean
* Aeration helps
* Sand, expanded clay, perlite, etc helps
* Sediment Filtration helps
* less Fish/Wildlife means less filtration needs

And yes a natural "polyculuture" pool is way way more complex than a monoculture sterile human only pool filled with 'pesticide/chloride". I don't think that there is only one way to build a natural pool, but I do like the idea of starting off with removed from nature and then slowly introducing more nature.

In your particular system. I would make with where the "swimming pool" overflow into the "growbed/filter area".
Then a sand filter pump is placed in the "filter/growbed area" and the "clean" water is sent up to the swimming pool.
The "outtake pipe" from the pool to the "growbed" area can also act like a swirl filter, sending all the sediments away.

David Pagan Butler, the author of Natural Swimming Pools answered some questions about the introduction of wildlife into natural swimming pools in this thread:

David Pagan Butler wrote:Hi Morana,
Generally most native animals that find their way in to a Natural Swimming Pool are welcome. Frogs are fine, and the occasional turtle may dig around and stir up sediments but shouldn't be a problem.

David Pagan Butler wrote:Hi Devon,
thank you for asking such good questions.
by "messing it up" I mean the following:

1) some fish will uproot plants. Plants are needed to condition the water in a Natural Swimming Pool.
2) fish stir up sediments, introducing nutrients contained within them into the water.
3) fish need feeding. This is bringing more and more nutrients into the closed system of the pool.

Nutrients lead to stronger plant growth. The plants most able to react to an influx of nutrients are algae. Single celled suspended algae make the water green and opaque. Filamentous algae form "blankets" over the surface.

In a large body of water, like a lake, with natural levels of fish stocks, the biology can cope with the increased nutrients so fish and swimming can coexist. In a smaller body of water, more of a swimming pool size, fish are not good swimming partners.

Paul Wheaton also talked a bit about about natural swimming pools in his book, Building a Better World in Your Backyard, and had that section of the audio book animated recently:

Parker - I'm no expert but based on my reading and studies of the subject (planning to build one myself), my understanding is that the water clarity all comes down to the nutrient balance that you can maintain in the pool with the plant life in the regeneration zone.  In simple terms, you want to be on the verge of starving the plants of nutrients so there is nothing left over to support algae growth in the swim zone.  Fish and animal activity increase the nutrient load on the system and although the plants will thrive - they may introduce more nutrient than the plants can remove and therefore leave excess in the water to feed biology (ie - algae/bacteria) that you don't want.  

The reason for nature "separation" is to manage the above principle in an intentional way.  The bog you refer to doesn't sound like it would work well as a regen zone due to the excessive nutrient load that it would introduce to your swim area.  If you don't want to lose that feature of your property though, maybe you can isolate and separate part of it with a liner and use it for regeneration.  

Hope this helps!

Cheers,
Anthony

Considering a natural pool on my wooded lot, I have questions about filtration area liners, wildlife interaction, water quality, and isolation levels. While I aim for a balanced approach, expert insights from Pools Now for Concrete Swimming Pool Installation in Florida would be invaluable. Can you guide these aspects?