My husband and I dug a pond this weekend it's about 20ft x 15ft and around 4 to 5 ft deep. We put a liner in and now we are not sure what to do about to water supply. Do you have to have a constent flow of freshwater to prevent it from becoming stagnent. I don't think there is a spring around the pond because when we dug no water rushed out of the ground. So does that mean we need to get a filter system to circulate the water? Please help we don't know what needs to be done. Thanks ssalapek