Over fifty years ago Denver Water “channelized” a lot of South Boulder Creek (SBC) by building high banks to reduce water evaporation in flood plains and also by removing any large structures (boulder piles, log jams, etc.). These actions allow water to flow rapidly and freely to Gross Reservoir which is designed to store water for use by the Front Range. In short, it reduced the population of native fish and also reduced the average size. But don’t get me wrong, Denver Water has actually turned what was naturally a small creek into a fairly stable flowing river that has an annual average of approximately 250 cfs when the Moffat Tunnel was built.
Over the past three years, sections of SBC have reversed the “channelization” process and focused a lot of effort on “stream improvements”. When re-structuring a section of river the main focus is to make drastic improvements to a specific stretch of water, but what actually happens is an improvement of an entire fishery, in this case, South Boulder Creek. The benefits of improvements can be seen far past the borders of private property. Improved streams will increase the fecundity rate of both aquatic insects and fish, create more suitable spawning habitat for native fish, and most importantly the development of deep winter lies which can sustain more and larger fish which will produce a healthier population.
A two mile section of river has recently been completely in a river system that naturally produced a mediocre fishery. The newly improved stretch is complete with adequate spawning habitat, proper runs and riffles for aquatic insect habitat along with an abundance of stream side vegetation for terrestrials, and good winter lies that will support countless fish of any size no matter the conditions.
The improved spawning habitat will attract fish for miles downstream which gives them something to look forward to during spawning time and it will also greatly improve the amount of age-0 fish which will disperse both upstream and downstream. The amount of insects in the river will increase with the improved habitat and not only in numbers, but also in size. And we all know what happens when fish have an endless buffet of large insects floating by them all day. Finally, the most important result from improvements is winter lies/pools. These deep slow runs allow fish to gather from miles away to lay low and lazy through the winter months which is the only way large fish can conserve energy and remain healthy. As the population begins to grow, fish become more nomadic and the two miles of improved habitat actually turns a ten mile stretch of water that can produce an abundance of larger than average fish on a regular basis.