Mud is everywhere. It’s in the ocean, lakes and rivers. It’s on the ground in forests and deserts. It’s even inside our bodies! Mud is made from tiny pieces of rock, sand, clay and other materials that have been broken down by water. The size of these pieces determines what kind of mud it is. Smaller pieces make silt, which you can find at the bottom of rivers or lakes. Larger pieces make gravel or sand which you can find along a beach or in a desert. There are many different colors of mud depending on what was originally in the water where it formed. Black mud comes from decaying plants like leaves and grasses that fall into lakes and ponds during autumn when there is less sunlight to help them grow green again. Greenish-brown mud comes from decaying plants mixed with dirt carried by rivers into lakes and ponds during spring floods. White or gray mud forms when large amounts of saltwater mix with fresh water creating layers that separate over time leaving behind a mixture of both colors . You may be wondering how all this mud gets onto your shoes? Well, most people think that rain makes their shoes muddy but actually rain does not cause much mud to form on roads or sidewalks . Rain washes away loose dirt already on the ground so it doesn't build up much unless something has already fallen onto the ground such as leaves or animal droppings . The real culprits are cars, bikes and feet! When these things move across the ground they pick up small particles of dirt making them dirty enough to stick to your shoes when you walk past them