This bridge is associated with the Great Northern Railway, not the Soo Line as suggested in the categories link.
The bridge is one of four similar bridges crossing navigable waters on the Leech Lake Indian Reservation. Two extensively modified bridges are still in service on the BNSF Railway near Ball Club, MN, crossing the Mississippi and Ball Club Rivers. A fourth bridge crossing Kabekona Bay on Leech Lake was removed decades ago, with the mechanism supposedly being reused on the Alaska Railroad; the pilings are still visible. Building and maintaining swing spans across navigable waters may have been a requirement of the Congressional grants of rights-of-way across the Indian Reservation.
During the late 1890s, the Steamboat River saw fairly heavy traffic. However, construction of this stretch of the Great Northern Railway in 1899 obviated the need for water transportation, and ironically, the swing span was only used a few times. Despite this, it was kept in working order as recently as the late 1940s.