"Have you ever wondered what McIntyre Creek looked like ten thousand years ago?"

Actually, I hadn't -- at least, not until Department of Fisheries and Oceans biologist Al von Finster asked me that question.

However, it soon became clear it's a question worth pondering.

Ten thousand years ago, von Finster says, the Whitehorse area was dramatically different. The Yukon River Valley was then the bottom of a large lake, so large that all of the area covered by modern Whitehorse was submerged.

The lake was fed by meltwater from the glaciers that buried most of the surrounding mountains and high plateau. In warmer months, raging streams poured off the glaciers, carrying rock shattered by the movement of monstrous icesheets.

One of those streams was the ancestor of McIntyre Creek. Today McIntyre Creek is a mild-mannered stream that meanders through wetlands in the western part of Whitehorse on its way to the Yukon River.

But its ancestor was a mountain-mover. It swept finely ground rock far out into the lake, where it settled to the bottom in layer upon compacted layer. It also carried larger rocks and gravel which piled up in huge delta. Yukon College and parts of the Takhini neighbourhood are built on the rock piles of the old delta.

Ironically, the legacy of that violent ancient creek is a series of small peaceful oases fed by the groundwater system the old creek left behind.

These aren't traditional desert oases -- green palm fronds in a sea of sand. Instead, they're a northern equivalent -- small patches of rainforest surrounded by the arid boreal forest of interior North America.

A mountain range and more from the ocean, you'll find plants that are common in the warm damp forests of the Pacific coast. Yellow monkeyflower is the most obvious indicator species, showing up as a lush carpet of gold in late spring and summer, says von Finster. Hairy gooseberry is another plant not found in the drier forest around the oases.

Animals are just as fond of the oases. Song birds gravitate to their shelter and to the rich variety of plant and animal food available there. The shallow streams and boggy vegetation support large and varied insect and invertebrate populations, which feed birds, fish and small mammals. The fish and small mammals, in turn, support predators like coyotes, and the vegetation and berry crops are popular with bears.

"These systems are little jewels," says von Finster.

The key to the systems is the groundwater. Water sinks into the piles of rock left behind by the ancient creek, gradually trickling downhill underground until it reemerges from the side of a bank or in a shallow depression. Water in a single stream might "sound" like a whale, diving below ground and reemerging several times on its way to the river.

Most of the groundwater that feeds the little oases of McIntyre Creek is what von Finster calls "sweet" groundwater. Because the softer rock that dissolves easily in water was ground up by the glaciers long ago and swept away, the groundwater moves through hard, non-reactive rock and emerges still full of the oxygen required to support aquatic life.

The other vital component of groundwater is heat. The groundwater feeding McIntyre Creek doesn't freeze. It sinks in through the rock during open water season, carrying with it the warmth of summer. The rocks soak up the heat and gradually release it back into the water over the winter.

That water warms the stream bottom through the winter and keeps the stream ice-free in places, increasing its oxygen uptake. Plants and animals that would perish if frozen survive and thrive in the groundwater's warmth.

"Welcome to paradise!" says von Finster, standing on the edge of a miniature wetland, lush green with moss, algae, and sprouting leaves. Only metres away, the last of the winter snow has turned to banks of ice, but here spring is well underway.

Von Finster measures the water temperature at a groundwater seep. It's fully two degrees warmer than meltwater flowing through another part of the creek. That temperature difference sustains a whole miniature world.

But it's a fragile world, says von Finster. Overuse could destroy it, or flooding, or diversion of the groundwater.

The City of Whitehorse has given McIntyre Creek's small oases some protection as a significant natural area, and the Kwanlin Dun First Nation has provided signs to help reduce disturbance to the salmon using the streams.

"These systems have been ten thousand years in the making," says von Finster. "It's our responsibility to be their stewards so that our children can appreciate them well into the future."

For more information about groundwater and aquatic habitat in the Yukon, contact the Department of Fisheries and Oceans at (867) 393-6721.