The main difference between rivers and lakes is in the water movement. A river basically moves, or it runs along its own bank. Rivers often flow in just one direction. While Lake, on the contrary, seems to be immobile, which is the reason they are often referred to as still bodies of water. If lakes ever seem to move, they move very slowly.
In fact, most times, their movements are influenced by the blowing of the wind. Another difference is that lakes and rivers are different in their appearance. Lakes are enclosed by land. Unlike ponds, they don't have a significant size to be considered as a lake. They are not connected to the seas or oceans, because they are actually inland.
Conversely, rivers are bodies of water with landmasses or very long stretches of land bordering their sides. Due to this, they are seen to be actually far longer than the lakes.