Channel between peninsula and island : Holgar Lake

There is a very large agressive fire all along the western shore of the lake. The fire has been burning for a week now and has produced lots of ash floating on surface. There is also what appears to be algae suspended throughout the water column. The ph seems very high compared to previous readings so I calibrated the meter again but still got the same reading. Could the ash or algae be increasing the ph?
Much of the burn is of relatively old growth jack pine stands with caribou moss ground cover.