Algae just the surface

STEVENS ISLAND -- For as long as I've been alive and likely for thousands of years beforehand, white pelicans have spent their summers on this narrow crescent of sand southwest of Grand Marais.

This little U-shaped island on Lake Winnipeg would appear unremarkable to a casual visitor. But it happens to be my favourite land mass on the planet, as I've spent a lifetime paddling up from the family cottage to observe it.

Over the decades, no development has come to the island to prevent pelicans and double-crested cormorants and ring-billed gulls from doing whatever it is they do all summer. Stevens Island and nearby Grand Marais -- the marsh, not the town -- are more or less protected areas, which of course does not mean too much when the ecology of the lake is in peril.

Earlier this week, when many Manitobans were wringing their hands about algae blooms on Lake Winnipeg, I wedged myself inside a borrowed kayak and paddled up to Stevens Island yet again.

First, I went to the southern edge of Grand Marais itself to check out the health of the marsh, which is in danger of drying up. This is not because of a lack of water -- Lake Winnipeg is in no danger of evaporating away like the Dead Sea -- but because of the complex interaction between introduced species and human changes to the lake's hydrology.

Paddling through the shallows along the marsh, I disturbed several common carp, the fat-bodied domesticated fish introduced to Manitoba about 125 years ago.

Carp like to splash around the shallows, where they voraciously consume the aquatic plants at the edges of the marsh. As they root around, they also stir up the shallow lake bottom and increase the turbidity -- that is, cloudiness -- of the lake water that's already become too cloudy because of too much algae.

Working in tandem with human beings, the carp are damaging the marshes, including my beloved Grand Marais. Water levels that used to vary greatly from year to year -- and thus allow fish to nibble at various elevations of vegetation -- are now kept at a relative constant by Manitoba Hydro, through the use of its Jenpeg generating station at northern edge of Lake Winnipeg.

The utility has long denied its dam has any deleterious effect, but fish biologists and lake ecologists believe otherwise. The constant activity of the carp at a single water level creates a visible shoreline rather than a gradual rise of vegetation from the lake.

A variety of land-dwelling but moisture-tolerant plants -- both native and invasive -- can then take root in the marsh and begin the slow process of converting it into a grassland. As I paddle along, I pass a single stand of purple loosestrife, a European invader that can crowd out cattails by producing three million seeds during a single season.

It only takes a few minutes to cross the narrow strait between the marsh and Stevens Island, which is noisy all summer due to the presence of several thousand nesting gulls.

The gulls grow louder if you approach them and will circle your boat in a comically menacing manner if you get too close. But I aim the kayak between the northern edge of the island and a small outcroppingwhere about 30 pelicans and a pair of herring gulls are waiting for fish to swim or float by and into their beaks.

The white pelicans, as always, are magnificent creatures. Roughly a third of the entire North American population summers in Manitoba and significant proportion of these birds do so on Lake Winnipeg.

For now, the fishing is excellent for the big waterfowl. Fish appear to be plentiful in the lake, as the old-timers in Gimli will tell you.

But this doesn't mean the lake is healthy. It may in fact suggest the opposite, as other lakes that suffer from eutrophication -- that is, an excess of nutrients -- experienced an explosion in edible fish numbers shortly before their fish populations crashed for good.

Lake Winnipeg is not toxic, although some of the blue-green algae may be at certain times. The real problem with the lake is over-fertilization from cities, farms, cottages, boats, sewage-treatment plants, factories and natural processes.

Too much phosphorus and nitrogen in the lake leads to too much algae, which bloom and die. The decomposing algae is digested by bacteria that suck oxygen out of the lake's lower depths, creating a low-oxygen environment that's hostile to most of the lake's other organisms, including fish.

The increasing temperature of the lake also aids algae growth and makes the environment less hospitable to cold-loving species such as whitefish. The increasing turbidity caused by the algae also makes life difficult for snails, freshwater mussels and other mollusks, whose numbers are now greatly reduced -- further depriving other organisms of food, and also reducing the filtration of the lake.

The entire food chain is out of whack, and even the most brilliant lake scientists concede they have no idea what will happen.

So despite the idyllic appearance of Stevens Island, Lake Winnipeg remains in trouble. The algae slicks that have garnered so much attention quite literally form the surface of the problem.

But for now, the pelicans remain.

bartley.kives@freepress.mb.ca

Republished from the Winnipeg Free Press print edition August 14, 2010 D9