A senior biologist with B.C.'s Ministry of Fish and Wildlife says an annual late-summer fishing ban is needed in the Merritt area to protect steelhead trout from the impacts of rising water temperatures.

The province temporarily shut down fishing on Spius Creek and the Nicola and Coldwater Rivers this week.

Bilologist Steven Maricle said water temperatures have reached nearly 27 degrees Celsius recently; the mortality rate of catch-and-release trout increases once temperatures rise above 20 degrees. 

"With the nature of the beast, climate change and all the rest of it, these systems are really susceptible," Maricle said.

Despite the high temperatures, Maricle said authorities haven't had any reports of trout dying because the fish appear to be finding cool pockets where groundwater is released.

"They do tend to survive even in these extreme temperatures, but they're really selective about where they hold and rear," he said.

He added that as the trout congregate in smaller, cool sections of rivers, they become easier prey for anglers.

"Catch-and-release would basically yank them right out of those refuge areas where they're staying cool and ... the stresses on them in these high temperatures would be potentially lethal," Maricle said.

The biologist said the Nicola River has historically been a concentrated area for these kinds of conditions, with water levels dropping consistently over the last decade.

This is the second year in a row the ministry has placed a ban on fishing. Maricle said his office wants the ban to be an annual event in the area for August and September.

With files from Jaimie Kehler.