TORONTO, Canada — Few would describe Toronto as a beautiful city. Its most distinctive architectural feature — red brick Victorian townhouses and mansions — have for years been losing the battle against the wrecker’s ball and green glass condo towers.

Thankfully, however, Toronto has been blessed by nature. Rivers and wooded ravines snake through the city and down to Lake Ontario. They are havens for wildlife and people.

One of the more spectacular bursts of nature in Canada’s biggest urban environment occurs every year around Canadian Thanksgiving. It’s the salmon run up the Humber River. And it’s a sight to behold.

The run last month, through the city’s west end, attracted avid anglers, giddy amateurs and onlookers like me, marveling at the sheer number and size of the salmon. The river was alive with them. Fishermen wading through the low running water could literally reach down and grab the salmon as they thrashed on the rocky riverbed to spawn.

The pros cast fly rods. The amateurs would stand above the salmon and lower baited hooks in front of their mouths. One group of youngsters scooped them up with a net, which must surely be illegal.

Hauling them out took time and effort. Anglers with bent rods zigzagged up and down the river until the exhausted fish could be heaved out of the water like logs. They were fat and almost three feet long — and that’s the truth.

Most were gently released, which was probably a good idea. Not only is it sporting, but the salmon have bulked up on the soup of chemicals and sewage in the Great Lakes. Those eagerly hauling them to shore generally spoke foreign languages, which perhaps suggests they were newcomers who hadn’t yet figured that out.

The Humber salmon run this year was in striking contrast to what has been happening on the other side of the country, on the Pacific coast.

The legendary sockeye run in British Columbia’s Fraser River has collapsed, its decline so steep and fast that Prime Minister Stephen Harper ordered a judicial inquiry Nov. 5 to find out what’s gone wrong.

The inquiry, to report by May 2011, was called after only 1 million sockeyes returned to spawn on the Fraser this fall. Between 10 million and 13 million had been expected. Scientists are using words like “disaster” to describe the turn of events.

The decline is particularly shocking because a healthy run was expected. In 2005, nearly 9 million sockeye spawned in the Fraser River. Two years later, an estimated 130 million young salmons, known as smolts, migrated to the ocean and millions were expected back to spawn this year. They never came.

The crisis isn’t restricted to the Fraser River. The fishing of wild salmon is a $185 million a year industry in British Columbia. But salmon catch along B.C.’s coast fell from 30,000 tonnes (33,000 tons) in 1998 to 5,000 tonnes (5,500 tons) last year. Commercial fishing is under threat. Worst off are native populations, who depend on salmon fishing for the little income they make.

An estimated 142 salmon populations along the B.C. coast have already been wiped out, never to return, according to the David Suzuki Foundation, a leading B.C.-based environmental group.

So what is happening? Some scientists suspect salmon farms are infesting smolts with sea lice. Salmon in these farms are packed in pens, creating a breeding environment for the parasites. The lice then cling to passing young salmon and burrow through their skin, consuming muscle and blood. In some coastal areas of B.C., sea lice are responsible for killing 80 percent of young salmon, the Sukuzi foundation estimates. (Watch a video about the repercussions of the salmon industry pushing into Chilean Patagonia.)

Others point to the impact of global warming on ocean waters, to pollution and to the paving over of habitat. But a recent report, by the Raincoast Conservation Foundation and academics from the University of California, points the finger at overfishing.

The report blames the Canadian government’s Department of Fisheries and Oceans for consistently overestimating the number of salmon and consistently allowing too much commercial and recreational fishing.

Canadians have seen this movie before. In 1992, one of the most abundant populations of cod in the world virtually disappeared off the Atlantic coast of Newfoundland. An industry that was the wealth of a province for 500 years was suddenly shut down, throwing 40,000 people out of work. It remains closed today.

Blame for the cod collapse was cast far and wide, from a jump in the cod-eating seal population to a change in the Atlantic Ocean’s ecosystem. But overfishing and a government slow to act were clearly part of the problem.

History, Canadians fear, is repeating itself.