Why do fish find it easy to swim in water yet you find it hard to walk through water?

Answer 1

It has to do with the amount of water you have to move in order to make distance.

A fish has what we call a stream-line shape. It presents a very small cross section to the water in the direction that it is moving in, therefore the entire mass of water that it has to displace is very small compared to the effort it makes. Most of the force it puts into motion is given to honest acceleration of its own body.

When you walk through water you present a very large surface area to the water and therefore have to move a large amount of water in order to effect distance.

Fish are specially designed to survive in a water environment. Their bodies are hydrodynamic, which allows them to cut through the water with little of no resistance. Their fins are designed specifically to propel the fish through the water. And most of all, fist have an internal ballast, which makes them buoyant enough to not sink to the lake/river/ocean bed, but not so buoyant that they float to the surface. The ballast is usually an air bladder, inside the fish, and it is meant to keep the fish within a certain water level.

A person, on the other hand, is not designed for aquatic environments. Humans usually wade into water, wearing clothing and boots, which get waterlogged and heavy. As most people don't have any thin surfaces, they are more susceptible to rushing currents, which make it hard to stay standing in running water. Finally, humans float, so when walking in deeper water, it become hard to remain upright or in contact with the lake/river/ocean bed.