How do fish appear in newly formed lakes and ponds?

How fish appear in a newly formed lake or pond depends a lot on where you are in the world.

In some very dry places, there are lakes that disappear for many months, or even for years. Some fish have evolved ways to survive exactly this kind of situation. Lungfish, for example, can live buried in sand or mud for years without open water. When the lake fills again, they wake up from aestivation, a survival state used during hot and dry conditions. It is similar to hibernation: their metabolism slows down, and they can wait until the environment becomes livable again.

Some fish do not survive the dry period as adults, but their eggs do. Certain species, such as African killifish, lay eggs deep in the bottom of temporary lakes or ponds. When the water disappears, the eggs can remain dormant in the mud. Then, when rain returns and the pond fills again, the eggs hatch and a new population appears.

In dry climates, seasonal rivers can also connect lakes that look isolated for most of the year. During floods or heavy rains, lakes and rivers may overflow, temporarily expand, and join with other bodies of water. Fish can then swim into new habitats before the water levels fall again.

Sometimes the connection is simply hidden. Dense vegetation, marshy land, or small streams can make separate ponds look disconnected when they are not. Underground rivers and underground lakes can also connect surface waters in ways that are not easy to see.

Some lakes and ponds are “new” only in appearance. They may have once been river meanders, floodplain pools, or parts of the sea or ocean that later became separated. In that case, fish may already have been there from the beginning.

Fish can also arrive through animals. Some fish eggs have adaptations that allow them to stick to wading birds or other animals. When those animals move between lakes, ponds, and rivers, they can carry the eggs with them. If the eggs end up in a suitable new habitat, they can hatch there.

Some fish eggs can travel in an even stranger way. In some Cyprinidae species, a fraction of eggs can pass unharmed through the digestive system of birds and come out in a different lake, pond, or river. Sometimes the eggs may still be inside the ovaries of fish that birds have eaten. This is similar to what happens with some plant seeds, which survive digestion and are spread by animals.

Fish do not always need to arrive as eggs. Some species, such as eels, can crawl short distances over land and reach another body of water. Birds can also accidentally drop prey into a different lake or pond. And in rare cases, fish can even be moved by weather. Waterspouts over shallow water can suck up small fish and carry them somewhere else, which is why reports of “raining fish” are strange but not completely impossible.

Humans, of course, can spread fish too, either deliberately or accidentally.

So yes, it may look weird when fish appear in a newly formed lake or pond. But it is not a miracle. Some survive drought, some survive as eggs, some swim through temporary connections, and some are carried by animals, storms, hidden waterways, or people. Nature has found many clever ways for fish to colonize new habitats.