Geoff Thomas: Trout supply is rich, but anglers need to watch rising river levels

A lone fly fisherman tries his luck on the Tongariro river in Turangi. Photo / NZH.

Anglers fly fishing on the Tongariro River are in danger of being trapped by rising river levels after deluges in the mountains. With rain in recent weeks described by local residents as "the heaviest, most concentrated rain we have ever seen", there is a real possibility of being trapped after wading out to fish from small islands and shingle banks when the river rises quickly.

Those anglers looking for quiet runs and riffles where trout may be holding and they have not been disturbed by other people will stalk the river banks and islands when the river is at normal levels. But a flash flood ran double the flow to 30 or 40 cumecs in a couple of hours, and anglers need to be aware of the danger when fishing on isolated spots and plan an escape route should they be caught out.

There have been no really big floods where it might reach 700 cumecs or more, and the largest so far this year has been around 200 cumecs. As a result of the stable river conditions through summer and into early winter the food supply for trout is very rich.

One trout was found to be so packed with caddis and dobson fly larvae that the stomach contents have been put on display at the Turangi tackle shop Sporting Life.

Fishing conditions have fluctuated as much as the river level, and it can be fishable one day and unfishable the next day.

But those anglers fishing downstream with wet lines and flies like Woolly Bugger and Rabbits do well as the water colour is clearing, and what is particularly noticeable this winter is the number of brown trout in the river. Usually larger than their rainbow cousins, these fish have been taken up to 4kg and when running up the river from the lake to spawn they are in prime condition.

The Tauranga-Taupo River will become dirty with rain, but the Waitahanui Stream remains fishable and those using glo-bugs by the main road bridge continue to catch fish.

Lake Taupo has risen a quarter of a metre which will help boaties negotiate the shallows, and trolling on the lake has been good at depths around 20m.

In Rotorua the spawning runs got off to a late start, but are now in full swing. Fish and Game have recorded about 500 trout through the trap on the Te Wairoa Stream on Lake Tarawera, which is a little lower than at this time last year. But the quality of the fish is better, with an average of 3.2kg and a lot of trout around 4kg.

The trout recorded at the trap are weighed and measured, and selected individuals are stripped of their eggs and milt for the breeding programme at the Ngongotaha Hatchery, which supplies yearlings for release into all of the lakes.

The most sought after adults for the breeding programme are wild fish, which make up about 30 per cent of the population in Tarawera, and anglers are required to release all male fish caught at the stream mouth, and females over 65cm. A mixture of three-year-old and four-year-old trout are stripped and eggs from hatchery-raised adults are mixed with those of wild trout, to keep the gene pool well mixed.

Weed beds are causing problems for anglers fishing in Ruato Bay on Lake Rotoiti, which is one of the prime release spots where adult fish return in winter and are caught by anglers. The solution is to use floating or slow-sinking lines and strip the line back in quickly over the weed.

Rotoiti still produces the largest trout but Lake Okataina and Tarawera are not far behind in terms of the condition and size of the mature fish.