The St. Croix River watershed is the premier mussel watershed of the Upper Mississippi River watershed, and one of the premier mussel watersheds of the world.
The winged mapleleaf mussel, a federally endangered species, is now found only in the St. Croix River.
Approximately 38 mussel species live in the St. Croix watershed (including the Namekagon River). Nearby northern rivers have good mussel numbers, but not the great numbers of the St. Croix. The Brule River, for example, a notably unspoiled river and watershed, has five or six mussel species. Of the 38 St. Croix species, 12 are on the Wisconsin Department of Natural Resources’ and 4 are on the Minnesota Department of Natural Resources’ state lists of endangered species. There are two Federal endangered mussels (Higgins’ eye and winged mapleleaf) and three special interest species in the St. Croix (spectacle case, snuffbox, and salamander mussels). According to scientific papers given in October 1992 at an international mussel symposium in St. Louis, MO, North America is the world’s great mussel continent; the richest species aggregations found in any watersheds worldwide are found in North America. North America’s best mussel watersheds have species numbers in the upper 30’s. Thus, with its 38 species, the St. Croix is among the world’s greatest mussel watersheds.
The uncommon richness of mussel species in the St. Croix parallels the uncommon richness of the flora and fauna of the watershed as a whole. The watershed has many uncommon Midwestern species, such as the cou¬gar; it also has wolves, bald eagles, peregrine falcons, and the Karner blue butterfly — all on the Federal list of threatened and endangered species. One expert characterized the St. Croix as a sanctuary containing the best-preserved (least human-impacted) remnant pre-settlement native communities in the Upper Mississippi drainage, and the very best preserved pre-settlement aquatic community in the Upper Mississippi drainage.
The main reason for light human alteration of the St. Croix landscape is the watershed’s generally mediocre agriculture potential — it has not been heavily farmed. Also, there has been little industrial development or mineral extraction and the area remains thinly populated. Water quality is excellent and un¬spoiled throughout the St. Croix — pre-settlement natural aquatic communities remain largely unaltered by pollution.
In a sense, the St. Croix watershed is an island of near-pre-settlement conditions surrounded by the more developed and altered North America of the Twentieth Century. Local popular sentiment, increasing involvement and commitment by state and Federal conservation and other agencies, and the Federal Wild and Scenic River designation of the Namekagon-St. Croix reflect the watershed’s value and offer practical vehi¬cles for protecting the watershed from what may be disastrous decimation of its mussel fauna should zebra mussels successfully invade.
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