What non-native fish species poses a threat to Colorado's native trout populations?

The correct answer is Lake Trout, which is known to pose a significant threat to Colorado's native trout populations. Lake Trout, being a non-native species, compete with native species such as the Colorado River cutthroat trout for food and habitat. Their introduction into certain areas has led to predation and competition that negatively impacts the survival and reproduction of native trout.

In contrast, Brown Trout and Rainbow Trout, while non-native, have established populations in many waters across Colorado and have coexisted alongside native species for a long time. Brook Trout, although they are considered non-native in many parts of Colorado, often reside in higher elevations or in specific ecosystems where they are less likely to have as direct an impact on the native trout populations compared to Lake Trout. Therefore, Lake Trout's aggressive nature and predation habits make it a significant concern for conservation efforts aimed at protecting Colorado's native trout.