This picture was taken near the end of the Cave and Basin Marsh Trail boardwalk. This trail gives visitors the unique opportunity to observe a marsh and wetland area without sinking to their knees in mud. The "ground" here isn't as solid as it appears in this photo because floating plants are hiding a lot of shallow running water. The branch of the boardwalk disappearing to the right leads to a wildlife viewing blind just off the edge of the picture.
Cave and Basin is the location of the hot springs that led to the establishment of Banff National Park and the Canadian national park system. This wetland is fed by warm water from those hot springs which are located on the hill above the marsh. Those hot springs keep the water in this marsh relatively warm the year around.
In fact, the water in this marsh is warm enough to support tropical fish. Mosquitofish from the Texas Gulf Coast were introduced to control mosquitos in 1924. In the middle of the 20th century, Banff residents who were tropical fish enthusiasts released numerous species in the marsh. Mosquitofish, Mollies, and African Jewelfish survived, reproduced, and thrived, especially the Mosquitofish. They can be seen in large numbers from the boardwalk.
Unfortunately, there is a downside to this story. There was a native fish that was endemic to the marsh, the Banff Longnosed Dace. Several factors may have led to its demise, but the introduction of the tropical fish sealed their fate. According to Wikipedia, the tropicals "reproduce year-round in the marsh, while the Banff longnose dace only spawned once a year. The exotic fish out-competed the dace for food and preyed on unhatched eggs." The Banff Longnosed Dace was declared extinct in 1987.
To reach the Cave and Basin area, drive south through downtown Banff, cross the Bow River bridge, and turn right on Cave Avenue. This site is 'Point of Interest Number 2' on this excellent Parks Canada map. Take time to visit the Cave and Basin historic area, and follow the signage down the hill to the marsh. There is also a nice hiking trail around the entire marsh area.
