Eating From Fresh Water

Which species pay, crayfish, eels, parasites and pollution

6 minIntermediateUpdated 2026-10-23 Eating From Fresh Water

You will learn

Pick the freshwater species worth the effort where you live
Handle crayfish legally and treat eels as protected
Judge whether a river is clean enough to eat from

⚠️ Never eat freshwater fish or crayfish raw or lightly cured. Cook to at least 63 degrees Celsius, or freeze at minus 20 degrees for seven days before any raw preparation.

⚠️ European eel is critically endangered and protected. Release it.

⚠️ Inland fishing, crayfish trapping and live transport are regulated locally. Check ICNF in Portugal, or your national inland fisheries authority, before taking anything.

Which species actually pay

Fresh water rarely feeds anyone on trophy fish. What feeds you is abundance you can take repeatedly: common carp, which grow large and are the most farmed freshwater fish on earth for good reason, tench, roach and bream from still water, trout where it runs cold and clean, and pike and perch as predators worth targeting where they are legal to keep. Perch is arguably the best eating fish in most European fresh water and is often abundant and unregarded. Effort per kilogram matters more than taste, so learn the two or three species your water holds in numbers and get good at those.

💡 One abundant species you can catch repeatedly beats five you catch once.

Crayfish, and the Portuguese exception

Crayfish are dense, easy protein taken in baited traps where that is permitted. The red swamp crayfish, Procambarus clarkii, is invasive across the Iberian Peninsula and much of southern Europe, established in nearly every warm slow Portuguese river. It is widely eaten and gathering it is often encouraged, but the rules still matter: transporting live invasive crayfish is illegal in many regions, so kill them at the water. Native white clawed crayfish are protected almost everywhere and must never be taken. Learn to tell them apart before you set anything, and check ICNF for the current position on trapping and transport.

💡 Kill invasive crayfish at the waterside. Moving them alive spreads them.

Eels are protected, not dinner

The European eel is critically endangered. Stocks have collapsed to a small fraction of historical levels, and eel fishing, keeping and sale are restricted or banned across the European Union with only tightly managed exceptions. Glass eel poaching is a serious offence. If you catch an eel on a line, unhook it in the water where you can and let it go. This matters beyond the law: an eel spends a decade or more in fresh water before one migration to spawn, so every adult removed is a whole breeding life gone. Treat it as a fish you will admire and release, permanently.

💡 Eel on the hook, eel back in the water. No exceptions.

Parasites in fresh water

Freshwater fish carry parasites that marine fish mostly do not, including the broad fish tapeworm and various flukes. The rule is simple: never eat freshwater fish raw, lightly cured or cold smoked. Cook it right through to at least 63 degrees Celsius in the thickest part, until the flesh is opaque and flakes from the bone. If you want it raw or nearly raw, the only safe route is freezing at minus 20 degrees Celsius for at least seven days, or minus 35 degrees for about twenty hours, and a normal domestic freezer often does not reach minus 20. Crayfish must always be cooked, never eaten raw.

💡 Freshwater fish, cooked through. Raw belongs to properly frozen sea fish.

Pollution and heavy metals

A river can look perfect and still be a bad food source. Old mining districts leave arsenic, lead and cadmium in sediment, and fish sitting in that sediment carry it. Industrial and landfill sites leave mercury and PCBs, which concentrate in fat and in older predators. Farm runoff brings nitrates and pesticide residue. Look upstream before you eat anything: mine workings, industrial estates, town outfalls, intensive farming. Many countries publish river specific consumption advisories, and where they exist they are worth more than any visual judgement. Where a river drains old mines, eat small young fish occasionally rather than large old predators regularly.

💡 Small young fish carry far less accumulated metal than big old ones.

Check yourself

Freshwater fish should never be eaten

Freshwater species carry tapeworms and flukes. Cook to 63 degrees Celsius, or freeze at minus 20 for seven days if it is to be eaten raw.

The European eel should be

Eel stocks have collapsed and fishing is restricted or banned across the EU. Unhook in the water and release.

Red swamp crayfish in Portugal are

Procambarus clarkii is invasive across Iberia. Gathering is often encouraged but live transport is commonly banned, so kill them at the water and check ICNF rules.

In a river draining old mine workings it is safer to eat

Heavy metals accumulate with age and up the food chain, so large old predators carry the heaviest load.

Try it for real: Audit one river

Pick a river or lake within half an hour of home and list the three species it holds in numbers
Trace it upstream on a map and note any mines, industry, landfill or intensive farming
Search your environment agency for a water quality classification or consumption advisory
Check with ICNF or your inland authority whether crayfish trapping is permitted there
Write a one page verdict on whether you would eat fish from it, and which ones