A pond can be as deep or as shallow as you like. However, you’ll need at least three to four feet of depth for fish like koi and goldfish. A good swimming pond will need at least that much depth as well to give you space to float and splash. For cooler water that technically functions more like a lake than a pond, you’ll want a depth of 6 feet or greater. This allows for the formation of a warmer top layer that is exposed to sunlight and a deeper layer of water that isn’t warmed by the sun. However, most ponds stay shallow enough that light penetrates to the bottom for better plant growth and a clearer view of the water feature.
Don’t assume that your pond will remain the exact depth you excavate in the beginning. If you want a pond that stays a minimum of 4 feet deep for years to come, you’ll likely need to dig to 6 to 7 feet deep instead. This creates more than enough space for underlayment, liners, layers of gravel or sand, and then all the muck that slowly builds up a natural pond. With a few extra feet to spare for these layers, you won’t need to dredge the pond every year just to keep the volume and depth at the level you need.
