Nutrient pollution is the discharge of excess nitrogen and phosphorus into water, mainly through fertiliser run-off from farmland, untreated sewage and detergents. The process it sets off is eutrophication.

The added nutrients remove the limit that normally restrains algal growth, so algae and phytoplankton multiply rapidly into a dense surface bloom — a harmful algal bloom. The consequences follow in sequence. The bloom mat blocks sunlight from reaching submerged plants and seagrass below, which die off. When the bloom itself dies, bacterial decomposition consumes the dissolved oxygen in the water, producing hypoxic "dead zones" in which fish and bottom-dwelling life suffocate. Some bloom-forming species also release toxins that kill marine animals and accumulate in shellfish.

Enhancing biodiversity is the reverse of what occurs. A bloom is dominated by a few fast-growing species and the oxygen crash that follows kills sensitive organisms, so diversity falls sharply.

Promoting coral reef growth is also wrong. Corals are adapted to nutrient-poor clear water; enrichment encourages algae that overgrow and smother the coral, and the reduced light impairs the symbiotic zooxanthellae the coral depends on.

Improving water quality is contradicted by the turbidity, oxygen depletion and toxin release that define the process.

Hence nutrient pollution triggers harmful algal blooms.