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With trout fishing season officially kicking off next week, many fly fishers will be gearing up to get out on the water. But some anglers are rethinking their approach as the waters that are favoured by trout are warming up and causing stress and even death of the fish.
Mike Weddell is a world professional title winner and five time British All Round Fly Casting Champion. Having lived and fished in Otago and Southland for nearly 40 years, Weddell has seen first-hand the ill-effects of the warming waters and low river levels.
He told Sunday Morning most of New Zealand's rivers are small and in lowland areas.
"Because there's not a lot of water in them, the water heats up quite quickly."
Warmer waters pose problems for trout fishing
Trout are most comfortable between 14 and 18 degrees, Weddell added. "That's the optimum for them growing and moving around and feeding."
He said you have to be careful even if you put the trout back.
"The water could be above the lethal level, which is maybe 25 degrees.
"What you should do is wade out to where the water is cooler and put the fish back there."
Native fish and insects and frogs are disappearing at quite an alarming rate, Weddell said.
"The insect populations are dropping, and that's due to what are euphemistically called pesticides on farms.
"They're not pesticides. They just kill everything. They don't just kill pests.
"The trout depend on insects. They feed on fairly small things.
"The greater the insect population, the better the trout do, and the lower the population, the worse they do."
Weddell said some rivers that had "really big populations" have also dropped - but it was not necessarily a bad thing.
"A river will only support a certain weight of fish. And if you've got thousands of them, they're going to be quite small."