Fish behaviour matters too, in koi and ornamental ponds. Fish gasping at the surface, gathering near inflows, or simply appearing less active than usual can be an early sign of an oxygen or water quality issue, though any specific fish health concern is a matter for a vet rather than a pond designer.

Algae is the single most common complaint from garden pond owners, and it is worth understanding why it appears before reaching for any particular fix. Algae is not really a pond disease, it is a natural response to conditions that favour rapid plant-like growth, and in most cases three factors are doing most of the work: light, nutrient load and plant balance.

Michael Wheat, Founder / Designer at Ponds by Michael Wheat, treats autumn debris management as one of the highest-value maintenance windows in the whole year, since the effort put in during a few autumn weeks tends to show up directly in how much algae trouble the pond has the following summer.

Plants that are failing rather than simply going dormant for the season is another sign worth noting. Marginal and oxygenating plants that are yellowing, rotting at the base or failing to establish year after year can indicate a water quality issue rather than a planting problem, and swapping plants without addressing the underlying cause tends to produce the same result again.

Light is often the most overlooked cause. A pond that receives direct sun for most of the day, particularly one with little floating or marginal plant cover, gives algae exactly what it needs to multiply quickly. This is why pond position and planting plan matter so much at the design stage, since a wildlife pond design and build service that is heavily shaded by trees brings its own leaf-litter problems, while one in full sun with no cover tends to run greener through summer.

Michael Wheat, Founder / Designer at Ponds by Michael Wheat, treats a stretch of unusual weather as one of the most useful times to book an audit, since it gives a clear, dated benchmark of the pond's condition right after a period of real stress, which is exactly when problems are most likely to be forming even if they are not yet visible.