I built my pond 6 years ago. I have a waterfall into a 15x6 with a small creek that ends with a 8x6. Pump at the end to feed waterfall. Each of the ponds are 2.5 feet deep. I have 8 gold fish and 5 small koi. The gold fish are all 4-6 years old, The koi I bought this year. I have a few water plants, lilly and hyacinth. I use barley straw to fight the algae. I love my pond.