The island became a popular tourist attraction in the early part of the 20th Century. It featured a bird sanctuary and was a very popular swimming hole. A causeway and bridge was built out to the island. Later, with the horse and buggy era giving way to the automobile, and Superior Bay becoming choked with sewage and pollution, tourists went elsewhere. The bridge over the railroad track collapsed, and the causeway bridge rotted into oblivion. The island itself began to sink, and it was almost gone by the 1950s.
The revival of Barker's Island began when the harbor was dredged deeper in the late 1950s. The sand from the dredging was again deposited at Barker's Island. The causeway was improved in the 1960s and tourist attractions started to locate on the island. The first was the Meteor, the last remaining whaleback ship, which has been open for tours since 1973. A marina, conference center, hotel, and housing has followed. More recently, the city of Superior added a park and charter boat dock, which has proven to be very successful. Barker's Island is now one of the top tourist destinations in Superior.
I haven't determined the specific date when the causeway to Barker's Island was built, bit it appears to be an early 1960s structure. The bridge is a relatively short steel girder structure about 22 feet long. It is flanked by water and sewer pipes on each side of the bridge. The causeway from the mainland runs approximately 375 feet before the bridge, and then another 300 feet from the bridge to Barker's Island.
The photo above is looking northwest towards the Barker's Island Causeway from a boat dock at a city park on Barker's Island. The Richard Bong Veterans Historical Center building is visible in the background. The photo below is a close view of the causeway bridge span, as seen from the same boat dock.