It joins Vancouver Island and much of the southern interior of B.C. — including the South Thompson, Similkameen, Kettle and Skagit areas — that have already been tagged with the highest possible drought rating.
A Level 4 classification means the area is extremely dry and further declines in stream, lake and aquifer levels could lead to water shortages and affect people, industry such as agriculture, wildlife and fish stocks.
It also means regional water managers may take additional regulatory actions if they are deemed necessary, such as the temporary suspension of water licences.
Angling was also suspended until Sept. 30 on the main stem of the Okanagan River between Okanagan Lake and Osoyoos Lake.
"The closure has been put in place to protect fish stocks at a time when they are vulnerable due to high water temperatures," the government said in a press release on Thursday.
The province says it hopes people in the area will conserve as much water as possible.