Library · Pollution & fish kills
Not every fish kill is pollution
Hot still weather, low oxygen and disease all kill fish — report it the same way and never guess at a cause.
Natural causes are real
A warm, still spell can pull the dissolved oxygen in a lough or slow river below what fish can stand — the same physics behind the summer dawn advice in The Why. High water temperature alone stresses trout long before it kills them, and disease can move through a population with no pollution anywhere near the water.
That is exactly why the rule is to report what you see, not what you suspect. The investigating agencies work out the cause — fisheries officers, the EPA and, where disease is suspected, the Marine Institute's fish health specialists.
What this means for your report
- Report a kill the same way whatever you think is behind it — the response starts identically.
- Never name a suspected cause, and never name a person, farm or business — a wrong guess can damage a real investigation.
- Dead water and gasping fish on a hot July morning still deserve the call: heat kills are recorded and matter too.
Related
Sources & how we know this (2)
- Low dissolved oxygen, high water temperature and disease are recognised causes of fish kills distinct from pollution; the national response begins the same way regardless
National Protocol for Coordinating the Response to Significant Fish Mortality Events in Freshwater — IFI and partner agencies, 2026 · 2026-07-17 - Warm, still weather drives overnight dissolved-oxygen sags that stress and can kill salmonids
LoughLogic research — when to fish: diel oxygen and timing (verified sources within) · 2026-07-17
Draft reference — pending review.