Goldfish require more oxygen dissolved into the water than plants alone can provide, even in a small pond. While fish may be fine for a few days to weeks in a well-planted pond with no pumps or filters, they’ll quickly foul the water beyond the system’s ability to recover naturally. Even a single goldfish in a large pond will overwhelm the water with its waste over time if there is no water exchange or pump and filter system. Fish ponds require filters and air pumps to keep the waste levels low and oxygen levels high.
Commit to the equipment you’ll need for the goldfish or choose to keep them indoors in an aquarium instead. Goldfish also like warm water, and very few parts of the country offer warm enough water even in the peak of the summer heat. You’ll likely need to install heaters in addition to the pumps and filters needed to keep the fish healthy. A fish pond may require more equipment and electricity than a completely natural pond with no koi or goldfish. However, they’re worth the effort and cost because there’s nothing like watching the playful flick of the glittering fins of your fish.
