Tropical Fish in the Snow

Now that winter is back again, we once more have the opportunity to see one of the world’s truly unique vistas…tropical fish in a snow bound lake. Yes, just 1½ hours from Calgary is the only place in the world that tropical aquarium fish live outside, wild, all year long, in a natural body of water that has snow around it. It is the marsh below the famous “Cave and Basin”, in Banff National Park, just west of the Banff townsite.

The Cave and Basin is an historic site and one of the major tourist attractions in Banff. The site was first brought to public attention in 1883 by William and Tom McCardell, and Frank McCabe; three railroad workers who followed a free-flowing stream (that was still warm to the touch in the middle of winter) up to its source: a collection of hot (well, warm) springs on the north side of Sulphur Mountain. One of these springs was in a small but lovely cave set in the cliff face. Two other springs were open to the sky. The men wanted to take ownership of the site and build a bathhouse/resort there. However, the federal government saw fit to intervene and used the feature as a cornerstone attraction for our first national park, which was incorporated in 1885.

The springs immediately became a popular swimming area. Warm, but not nearly as hot as the springs on the mountain’s eastern flanks, the Cave and Basin springs were a popular place of recreation. The warmest spring (in the cave) was a famous “medicinal” spring. The coolest spring, with a temperature of about 27C, could be used for a refreshing swim on a hot day, without being brain-numbingly cold like the typical mountain lake is in even the hottest summer.

A resort was built on the site in 1886, to be later expanded in 1932. But, although the resort was commercially successful, even the hardest nosed capitalist would be hard pressed to call this development an improvement in any sense of the word. It must be remembered however that the primary purpose of the national parks at that time was recreation, not conservation. Banff was (as the park’s historians like to say) an island of civilization in a sea of wilderness, and development – any development – was welcome. But nowadays the park is an island of wilderness in a sea of civilization, and development threatens the very thing that the tourists come to see. And in the case of the Cave and Basin, all natural beauty is long gone. The Cave is now just a room in the resort building and even the exterior springs are surrounded by walls. Sigh.

The desecration of these natural wonders was more than just an aesthetic loss, as unnoticed in the springs lived a small, rather non-descript, pond snail. The Banff Springs snail (Physella johnsoni) was originally endemic to five springs and their outflow streams near Sulphur Mountain. It was known to occur in the Upper Hot Springs, Kidney Spring, Middle Springs, the Cave and Basin, Vermilion Lakes Spring, and a warm stream near the Banff Springs Hotel. Now they are found only in one of the Cave and Basin springs, its outflow stream, and the Cave and Basin marsh below the spring. The reason for its disappearance in the other locations is believed to be development and human disturbance of the algal mats upon which the snail feeds. Now all swimming in the Cave and Basin is forbidden in order to preserve the species, and so the resort has lost its original reason for existence. Today it is a museum and interpretive center.

Compared to the springs themselves, the stream and marsh below the Cave and Basin are relatively pristine “warm water” ecosystems. However, human interference has been at work here too, as residents of Banff released a variety of tropical fish into the marsh after the war years (no one seems to know exactly when this happened). At one time or another, angelfish, guppies, and tetras have all been spotted in the marsh, but these failed to thrive and are probably no longer present. Now there are three introduced tropical fish species known to live in the marsh; Gambusia affinis (the mosquitofish), Poecilia latipinna (the sailfin mollie), and Hemichromis bimaculatus (the jewel cichlid).

Getting to the see these fish is easy – the route to the Cave and Basin is well signed. Follow the main drag through the town of Banff west until you cross the Bow River, then turn right. Head down the road another mile. From the Cave and Basin parking lot, walk up to the main building and around to the north side. Take the “Discovery Trail” north of the main building (there is no reason to actually enter the building). A boardwalk goes down to the marsh, culminating in a “fish-watching” platform.

Along the way take note of the white algae growing in the springs’ outlet stream. I found this stuff fascinating (how does it photosynthesize without pigment?) but could not find out anything about its biology.

Be careful heading down the boardwalk as it can be icy in winter. On really cold days fog shrouds the marsh, making the scene very otherworldly, but although beautiful, the fog doesn’t help you find any fish. The best place to see the fish is (not surprisingly) the fish-watching platform. Lie quietly on the platform with your head over the side, and in a few moments the fish will reappear. Pretty much all of the fish you see will be introduced tropicals.

Personally, I found the mollies a bit of a disappointment. They are much smaller than well-fed aquarium specimens. And although all were originally black, they have over the generations reverted to their original spotted coloration. So from the top (looking down on their backs) they aren’t too impressive. I saw one male however with a lovely sail fin and a pleasant yellow cast to its fins. Quite nice. The jewel cichlids are also small (about 6cm) but feisty and in nice color. And the male mosquito fish court like male mosquito fish do.

Although the tropical fish are introduced, they now enjoy the full protection of the national park authority. You can not legally catch, keep, feed, or unduly disturb them.

It is hard for a tropical fish enthusiast to not to be impressed by seeing these fish in the snow, but it must be remembered that they are introduced species that had a profound impact on the native fishes of the marsh. The marsh was once the only home of the Banff longnose dace (Rhinichthys cataractae smithi), which was declared extinct in 1986. It is highly likely that it was competition with the introduced species that led to its extinction.

So enjoy a walk through the marsh on a winter’s day. But give a thought to what we have lost to greed and ignorance.



Nelson, J.S. 1983b. The tropical fish fauna in Cave and Basin Hotsprings drainage, Banff National Park. Can. Field-Nat. 97(3): 255-261 ?