From a general rafting standpoint, the water on the Lower Kern River is warm and you will not need a wetsuit. The water on the Upper Kern River can be chilly though, and you may need a wetsuit in March, April and May. In June and July, it can be warm enough where one is not needed. Again, this is giving an answer with a broad paintbrush, with more exact information below.
Upper Kern River water temperature
When I first started digging into this question, I was pretty confident I would be able to find a USGS gauge that was tracking water temperature. What’s interesting, is that none currently exists, which I would say is pretty unusual for a river that sees this much use. After plenty of searching, I was able to find an old gauge that took daily Upper Kern water temperature readings from 1980 through 1988. This gauge was located near Kernville. I’ve averaged and summarised the data below by month. It is my belief that while this data is considered old, that current water temperatures on the Upper Kern should be close to what is listed below. If anything, current water temperatures will be slightly higher.
Upper Kern River – Average Water Temperature (Fahrenheit)
Lower Kern River water temperature
Despite Lake Isabella being filled by the chilly Upper Kern River, the lake is pretty warm. It’s a shallow lake, and during the summer months, it gets hot around here, with many weeks hanging around 100 degrees. This translates to a lake that’s easy to warm, and then as they release that water, a comfortable Lower Kern River.
When I found that old river gauge on the Upper Kern, I was confident that I would find one on the Lower Kern as well. It’s odd, but nothing ever surfaced. Even asking around, no one had any good idea. I knew the water was warm, but any sense of exactly how warm, I had no clue and it appeared no one else had ever bothered to measure it. So I’ve decided to measure it. I bought a digital reader, and as often as I can, I’ll be measuring it at the same place and recording the water temperature. Sure, it’s not the most scientific method, but at least it’s some sort of data that we can look at.