The majority of lakes found in Olympic were formed by gouging glaciers. Large lowland lakes, such as Ozette and Lake Crescent, were dug by huge continental ice sheets that poured out of Canada over 13,000 years ago. Smaller highcountry lakes and tarns were carved by alpine glaciers. As the ice melted away, the eroded depressions filled with meltwater.
After the Ice
As Olympic's waters warmed, many forms of aquatic life began seeking the freshwater of Olympic's lakes and streams. They started breeding in coastal rivers and lakes. Generation after generation, insects, amphibians and fish populations stair-stepped their biology into Olympic's heart. The habitat and migrations of water-confined organisms such as fish is defined by waterfalls, steep cascades and other physical barriers. Unlike fish, organisms such as amphibians and insects can live both in and out of water. These semi-aquatic organisms will traverse around steep waterfalls and reach most of Olympic's highest lakes. Although historically absent from highcountry lakes, non-native fish have subsequently been introduced into these calm waters disrupting the ecology of these special places.