Water temperature has direct and indirect effects on nearly all aspects of stream ecology. Largely because temperature plays a major role in determining the amount of oxygen that can be dissolved in water, and everything alive in a stream breathes oxygen.
Cold water can hold much more oxygen than warm water, so aquatic invertebrates and fish with high oxygen demands (the organisms native to the Jocko River) are found only in these waters.
When dissolved oxygen concentrations drop, species that need high concentrations of oxygen—mayfly and stonefly nymphs, caddisfly larvae, and bull trout and westslope cutthroat trout—will move out or die, replaced by organisms like sludge worms, blackfly larvae, and leeches, which can tolerate lower dissolved oxygen concentrations.
How cold is the water in a pristine Montana stream? What you consider cold might be hot enough to kill a bull trout. The scale at the bottom of each of the charts below (click on the image to expand it) show human survival times in cold water as determined by the Red Cross. Compare that with the habitat requirements of the various species' below to see how they compare to your perception of cold.
   Click to expand any of these images
   Click to expand any of these images
Water temperature has direct and indirect effects on nearly all aspects of stream ecology. Largely because temperature plays a major role in determining the amount of oxygen that can be dissolved in water, and everything alive in a stream breathes oxygen.
Cold water can hold much more oxygen than warm water, so aquatic invertebrates and fish with high oxygen demands (the organisms native to the Jocko River) are found only in these waters.
When dissolved oxygen concentrations drop, species that need high concentrations of oxygen—mayfly and stonefly nymphs, caddisfly larvae, and bull trout and westslope cutthroat trout—will move out or die, replaced by organisms like sludge worms, blackfly larvae, and leeches, which can tolerate lower dissolved oxygen concentrations.
How cold is the water in a pristine Montana stream? What you consider cold might be hot enough to kill a bull trout. The scale at the bottom of each of the charts below (click on the image to expand it) show human survival times in cold water as determined by the Red Cross. Compare that with the habitat requirements of the various species' below to see how they compare to your perception of cold.
   Click to expand any of these images