An ecosystem like the Colorado River evolved over thousands of years and includes myriad species adapted to that specific environment. However, through accidental and purposeful actions of humans, non-native species have been introduced in the ecosystem. Some of those non-native species have flourished, to the detriment of native species and to the river itself. As two examples:
- Non-native fish species such as trout actually eat native endangered species like the humpback chub. This predation by non-native trout is one of the reasons why humpback chub recovery efforts have faltered and stalled.
- Tamarisk, a non-native bush, was introduced to stabilize banks along the river, but ended up taking over miles of river bank, using extraordinary amounts of water, and changing the soil chemistry of the native riverbank thus pushing out native vegetation and wildlife.
Other non-native species that have had a negative impact on the river and the ecosystem includes giant cane, zeebra and quagga mussels, wild pigs, burros, Russian olives, and cheat grass are examples of accidental releases. Land and water managers have spent many millions of dollars trying to control invasive species impacts – expenditures are ongoing for the foreseeable future.