CFS and How it Affects Fish

First of all, what is CFS? CFS refers to cubic feet per second, and it is used to measure river flow. That being said, we can already start thinking back to times when we fished high water, low water, average water, and the relation to where fish were holding in the hole during each water level. I could write a book on this subject, so trying to cram it into the few hundred words of a blog has some difficulties, but what we can do is open the door and shed some light on a few basic principles.

High Water
High water is great at moving food sources from common areas and depositing it into areas that can be sneaky or areas that are typically not underwater. Trout will move out of the heavy current seeking the newly relocated food source. If the water levels continue to rise or begin to fall the food caches will also move along with the trout. This can happen over a period of a few days or in some extreme circumstances, a day.

Our anadromous friends could care less about where food is being deposited but love taking the path of least resistance upriver to their spawning grounds. Standard running lanes may have too much water pumping through them, detouring salmon to move tight to shore or find structural elements that are typically too shallow or even out of water during normal water flow.

Low Water
Low water definitely channels fish into a few obvious places, making the where-are-they aspect pretty easy. If you fish popular water like the Kenai everyone has a rough idea where the fish will be. Pressure can ruin even the hungriest trout’s appetite and will push them into very weird places where there may not be a ton of food, but at least they can eat without getting a hook in the face. Low water equals time to get creative and sneaky.

Salmon react similarly to trout when water levels are down. They spook easy and only have a few places to hide. You will notice their travel patterns become erratic as well as their bite behavior. Low water and sun is a nightmare to most salmon enthusiasts

Water Temp
If you notice a large change in water level in a short period of time you can assume the water temp has changed dramatically as well. A couple degrees of change will alter the bite for trout or demolish it completely. No worries, trout have to eat to survive but it may take a day or two for them to acclimate to the new water temp in order to put on the feed bag again.

Since salmon aren’t feeding we can take that out of the equation, but sudden changes in water temp will alter their aggression and movement cycles upriver, causing a decline in the bite. I have noticed salmon to be more resilient to water-temp fluctuation over trout.

Piecing together CFS, water temp and bite flux takes time and many days on the water spent analyzing the current conditions and how they might change or have changed, and then relating it all to fish behavior. The good part is all you have to do is go fishing more!