These two phrases have the same meaning. They describe how the streambed is full of ice and snow in the winter. Alternate translation: "which look dark in the winter because they are covered with ice and are full of melted snow" (See: [[rc://en/ta/man/translate/figs-parallelism]] and [[rc://en/ta/man/translate/figs-explicit]])
This speaks of the snow melting and the water going into the streambed as if the snow were hiding in the streambed. Alternate translation: "because the snow melts and goes into them" (See: [[rc://en/ta/man/translate/figs-personification]])