Just about every farm has a pond somewhere on its property. Usually, they did not have a farm and then make a pond. Instead they first found a source of water such as a stream and then built their farm near it. Most farms were nowhere close to public water supplies and so farmers had to plan for their own water source. If you have a stream on your property, there is a good possibility you can construct a farm pond.
Look at the lay of the land along the stream. You will need to find an area where the sides are pretty high and with a little reinforcement could hold in the water. The more the land can hold the water, the less work you will have to do. Generally, it will need to be at least 4 feet deep to not dry up during high heat in the summer.
Decide where you want to form a break in the stream flow. You will need to check soils to make sure you have enough clay content to hold the water. When you squeeze a damp handful, it needs to hold together and not just crumble. Soil with too much gravel or sand will just not hold the water. Also check to make sure that if your pond overflows during a heavy rain other land will not be in danger of washout.
Check to see how much soil will need to be removed from the bed of the pond. If you don't have a large pond to build, a simple shovel will work fine, although it will be some hard work. Larger ponds will need the use of a backhoe. Typically, the soil used from the bottom of the pond can be moved to help create the higher sides.
Remove and trees, shrubs and plants from the top layer of soil. Clear the topsoil and set it aside for use later. Remove the soil from the center of the pond and build up the outer edges of the pond so the water can be contained. Save as many plants as you can for planting around the pond to help prevent erosion.
Keep the pond on the side of the stream instead of in the middle if at all possible. This will keep the flood waters after heavy rains from dumping heavy amounts of silt into your pond and washing away any fish that you have collected in the pond. A partial dam in the stream will raise the water level enough to flow into your pond.
Break through the side of the stream so the water will naturally flow into the lower area of your pond. You will need the pond to be level with the surface of the stream when it is filled up, or you will dry up the stream bed downstream. Add a good amount of rip rap or rock to keep the opening from filling up with sludge.
Plant grasses and plants around the edges of the pond to keep it from eroding.