Imagine that I built a concrete-walled pool the size of a football field and filled it with fresh water - obtained from another lake but free of bacteria, plantlife, eggs, etc.

Would it ever, over time, become a life-filled "lake" - with fish, amphibians, algae, plants and other water-dwellers?

If yes, how?

What would the chain of events look like? I'm assume plant-life would get there first but how would it develop an established eco-system?

Please re-tag as appropriate as I am new to this SE site.

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    $\begingroup$ The short answer would be yes, given enough (long++) time. The situation would be similar to e.g. newly formed volcanic islands or when bare rock is exposed after a glacier disappears. However, the specifics are really hard to answer and would depend on the geographical location and stochastic colonization events, and you won't get a definite answer on a Q&A. Look into the vast ecological litterature on colonization and succession. A likely chain of organisms would be someth. like: Bacteria & phytoplankton-> zooplankton-> invertebrates & plants-> vertebrates (e.g. birds and amfibians first). $\endgroup$ Commented Oct 3, 2013 at 10:01
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    $\begingroup$ Also look at Hydrosere succession, which describes long term succession in fresh water bodies. $\endgroup$ Commented Oct 3, 2013 at 10:03
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    $\begingroup$ @fileunderwater Assuming that you don't also build a bunker around the pool, and that you live near or in the path of migrating species (especially birds, and you probably do), it actually doesn't take long at all. Higher level animals are going to land/bathe/drink it, as they do they are going to bring a whole host of life with them, including the possibility of fish through eggs. $\endgroup$
    – Atl LED
    Commented Oct 4, 2013 at 3:18
  • $\begingroup$ @AtlLED The "long++" part was referring to fish. I agree that birds and flying insects will visit quickly (they will spot a fotball-field sized pool). I read the questions mostly as asking whether a natural lake ecosystem will develop over time. $\endgroup$ Commented Oct 4, 2013 at 6:15
  • $\begingroup$ If the pool was stagnant, I can imagine that algal spores would be among the first to reach the lake. The algae could 'suffocate' the lake and make it very cold and even poisonous if certain species of algae bloom. I hope one/some of the answers discusses this. $\endgroup$
    – James
    Commented Oct 5, 2013 at 20:22

3 Answers 3


if the pool were just sitting out in open air, on earth and all that good stuff, it certainly would, given enough time.

This thought experiment is in the same vein that inspired Darwin when he reflected on his experiences on his visit to the Galapagos islands.

Think about it - the many islands which are formed by upheaval were lifeless when they first emerged from the ocean. Over time, the winds or storms eventually populated them all - just about every island has animal life on it. Not all animal types are found there that are best for the climate; its a matter of accident that some birds or lizards are found on the galapagos islands. These accidental landings don't happen very often and sometimes a single animal will generate many species which will fill the role that other animals would normally fill on the mainland continents at the same latitude.

This is what happened on the islands- in different islands, Darwin found finches of sizes and shapes would be eating insects from bark or ant hills that might be done by an animal

Eventually, if you wait long enough a frog, then maybe a couple of fish will find their way into the pool from a nearby waterway (yeah that could take a long time I know). If it takes too long then a new species will show up. If you build walls around the pool it might not happen. These accidents of animals showing up by accident can take millions of years.

This experience of Darwins' has inspired an entire field of biology - Island biogeography. Each island is an experiment and ecological niches can be observed by taking a series of islands and seeing how different animals take up the various ecological roles on each. A famous experiment EO Wilson and colleagues did was to fumigate some mangrove islands and watching them repopulate.


I recently dug a pond in a forest, and the first things to happen was not actually plant life. First I found small aquatic animals that lived in the mud, then I found salamander axolotyls and water striders, and crawdads. Salamanders (especially newts), water striders, and crawdads all migrate between ponds to breed and when old ones dry up, as well as various other aquatic animals. The aquatic mud dwellers might have been washed there by rain, or they might have migrated there like the others. In the case of a lake, all of these will happen, although slower because of a lack of sediment with concrete walls. The fish would depend on whether or not there is a waterway connecting the lake to an area where fish already live. These events would happen in the first year except for fish, and pretty soon algae will be growing right after the animals moved, or during, and plants will start to grow as well, their seeds or whatever they use to spread will make their way to the lake. I have found though that lakes, especially man made ones, often contain very little large plant life. As for the time it takes, one year will start it off with basic predator prey relationships, and will slowly grow from there over the course of years.

  • $\begingroup$ I believe that's why the question used concrete, to avoid the fact that a pond/lake in the dirt is actually still quite open and in contact with life. $\endgroup$
    – Amory
    Commented Oct 3, 2013 at 15:07
  • $\begingroup$ I did mention the fact that it would occur slower with concrete, but eventually enough debris would fall in the water that there would be sediment. $\endgroup$
    – Tzacol
    Commented Oct 6, 2013 at 17:31

The answer is yes, absolutelyvne enough time. You can do this experiment yourself. Get a clean glass jar, hell even sterilize if if you like (your oven overnight at 250 F will do it). Fill it about 3/4 with clean (or even sterilized) water, and leave it outside in a mixed sunny shady spot for a few weeks, in moderate weather. It's small volume will get cooked by constant direct sun, which will impede the results. After a few weeks (might be faster), look closely into the water (through the sides of the jar) with a magnifying glass, or better still, sample the water and look under a microscope. You won't see, but they are there, multiple bacterial species. You will see single celled algae, small pond creatures (hydra, rotary-topped species (multiple)), paramecia, and multi-celled algal forms in strings. These are all fallen in from airborne dust and windblown particles. You likely won't get fish, but if you are lucky, you might get a few brine shrimp. And yes, particles of blown or bird-carried dirt etc can easily carry shrimp, amphibian, or plausibly, viable fish eggs.

But what do they feed on? There's no food in the water you put in !! CO2, nitrogen, Oxygen, etc are readily available from the air. A few cells of bacteria or algal forms seed the clean water, and begin fixing CO2, nitrogen etc, and now you have a food source. Wind-carried (or bird-carried) small organisms can now survive in a web of bacteria-plant-animal interactions. By the way, you can also run a control jar, where you sterilize the jar, fill it with boiling hot water, and quickly cover it tightly with foil. Place it beside your open jar, and it will grow...nothing.

As a side note, "toxic" algae are often not toxic to small organisms and other algae. Their toxins (neurotoxins usually) affect mostly only higher organisms, such as fish and humans. Algal blooms kill fish and birds, they seldom sterilize the pond.


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