A deadly combination of low water levels and warm temperatures has led to more than 1,000 pink salmon dying in the Tsolum River in the Comox Valley.
Caroline Heim, program co-ordinator for the Tsolum River Restoration Society said low flows have prevented fish from moving freely upstream and have created a bottleneck situation where they consume all available oxygen and eventually die.
Additionally, the current water temperature is around 21C; however, Heim said during the summer heatwave in the Valley, water temperature rose to 29C.
“The fish are dying later in the day because the water collects heat during the day and is its warmest in the late afternoon and early evening.”
When there is rainfall in the Comox Valley, the Tsolum generally responds very quickly and rises. The lack of rainfall is one of the major factors contributing to the low water levels, she noted. There are also a number of water licences for agricultural use which draw water from the river, but generally, those licences limit use until the end of July.
Unlike the Puntledge River, the Tsolum is not a dammed river. The Tsolum is fed mostly by wetlands, lakes and the snowmelt and while there is a dam at Wolf Lake which feeds into Headquarters Creek and eventually into the Tsolum River, water levels have to be carefully balanced, explained Heim.
“It’s pretty stressful for fisheries managers as there has to be enough water in Wolf Lake and in the Tsolum. Every year is different, and this is probably one of the hardest years coupled with such a large return (of salmon).”
She noted looking ahead if low water levels coupled with hot temperatures are the ‘new normal,’ various factors such as the number of water licences may have to be further examined.