While it is probably fair to say that any pond-feature in a garden could be called a water garden, not every water garden provides a home for fish, although “water garden” and “fish pond” are used interchangeably so commonly that the distinction between them is often lost.
However, having fish in a pond has consequences for many other aspects of its upkeep and management – as well as dictating what else can sensibly share it with them – so the difference does matter. While fish undoubtedly add a whole new dimension to the garden pond, keeping them healthy and the water feature itself in good condition requires an understanding of their needs and the demands they make of their surroundings.
For one thing, adding fish to a pond changes its most fundamental feature – the water. Fish naturally turn something in the region of five per cent of the food they eat into ammonia which they excrete; the greater the numbers, the larger the amount of ammonia excreted, polluting the water day by day. To keep fish healthy, the ammonia levels need to be kept to as near zero as possible – against the constant tide of the stuff being newly produced.
While a good bio-filter is more than capable of achieving this, turning the ammonia into first nitrites and then nitrates – useful plant fertiliser – the situation is further complicated by the need for open water in the fish pond. These high levels of nitrates, coupled with more created from uneaten food as it breaks down and available light filtering unrestricted through the water, provide ideal conditions for the growth of algae, leading to the possibility of blooms of “green water” or blanket weed. Again, there are solutions to these problems too, but the whole matter of fish keeping leans heavily on technology to provide a balanced environment in the very limited space of the garden pond – however large it may be.
Plants and Wildlife
The “true” fish pond is first and foremost a place for fins, not fronds. Though plants may, of course, have a place here, they will always be secondary to the main event – supporting actors to the stars of the show. While a fish-less water garden can be created with internal contours and depths to suit the desired planting regime, enabling marginals in particular to be shown off to their best advantage, the design of the typical fish pond imposes some serious limitations in this direction. Accommodating deep water plants is not normally a problem, but the usual narrow shelf for bog plants leaves little scope for anything more imaginative than planting them like a row of soldiers along the edge. It may leave more water for the fish, but protruding planting baskets do little for the overall visual appeal.
The situation is even more clear-cut if your idea of water gardening includes attracting wildlife. Although the huge loss of wetlands from our countryside in recent years has forced nature to become very good at making use of any available resource, all ponds are not the same and the “ideal” wildlife pond differs from a typical fish pond in many important ways. It is not just about depth, filtration and planting; whether it is hungry goldfish hoovering up tadpoles and froglets or herons making a meal of your prized koi, fish and wildlife simply do not mix well in the same small body of water.
Of course, it is perfectly possible to enjoy fish, plants and wildlife in the same garden – if not always in the same pond, so one solution to any conflicts is to simply construct a second one. Pond building can become an addictive pastime!