Stream Fragmentation

by mstev3 on April 17, 2015 - 11:54am

Stream fragmentation is a serious issue that can have a negative impact on fish communities within the stream. Fragmentation is caused by human alterations, such as when dams are built. This separates sections of streams and does not allow fish to move upstream or downstream as needed. This is particularly important with anadromous species such as salmonids. Salmon will use homing capabilities to find their way back to their native stream for spawning. When dams are built this prevents the salmon from moving upstream which in turn can prevent them from spawning; entire generations of salmon have been lost to this. Fish ladders and other techniques to help fish bypass dams have been built but are not as effective as a natural unaltered stream. Human alterations to streams have also slowed the flow rate which can disrupt stream equilibrium. Slowing the stream flow rate can cause issues for fish health as well. Another issue with stream fragmentation that was interesting is length of the fragment of stream. Certain sections of streams can be fragmented too short, which can cause an over population of fish in a small section. This increases competition for habitat and food and will disrupt the fish community. A study conducted in the Great Plains region of the United States showed the effects of stream fragmentation. The team analyzed community composition, species population status, fragment size and flow patterns for 60 stream fragments spanning the latitudinal range of the United States. They found that stream fragment lengths were a strong predictor of conservation status, explaining 71 percent of population declines. As the need for freshwater continues to grow, especially with the California situation, more dams will be built but there needs to be an understanding of the effects dams have on stream equilibrium and the fish communities that live there. Conservation measures that restore connectivity of river fragments and natural flow patterns will likely benefit stream spawning fish, but may decline the amount of available freshwater that can be used. Finding the balance of having a healthy stream ecosystem and sufficient available freshwater is tricky but is necessary to keep the ecosystem healthy as a whole.


Gido, K. 2010. Consequences of stream fragmentation and climate change for rare Great Plain fishes. Great Plains Landscape Conservaton Cooperative. pp: 1-35.

Perkin, J., S. and K., B., Gido. 2012. Fragmentation alters stream fish community structure in dendritic ecological networks. Ecological Application. Vol. 28: No. 8. pp: 2176-2187.

Vermont Rivers Program. 2011. Introduction to Dynamic Equilibrium. Vermont Agency of Natural Resources. (1): 1-4.


About the author

I am currently an undergraduate in environmental science at The College at Brockport: State University of New York. I study both aquatic and terrestrial ecology with a passion for fisheries.