My Watermark is Mimico Creek, Ontario.

When I was between 10 and 13 years old, the Mimico Creek in the west end of Toronto was my playground, my refuge, the place where my dreams of adventure came true.

It's quite unremarkable, a mere slip of a stream, easily fordable. It meanders from north of Pearson International Airport about 30 km in a generally south-east direction to Lake Ontario.

These days it's completely urban. It's crisscrossed by busy roads and highways, flanked by apartment buildings, suburbs, 3 golf courses, schools, parking lots, baseball diamonds and redirected by concrete spillways. These all affect the quality of the water, and yet it thrives for the most part.

It is an oasis of parkland, walking trails and bridges with an assortment of animals, birds and fish living in its shadow. There are even a few deer. All this despite the continuous urban onslaught and a history of industrial pollution dating back to the 1950's when I saw it die.

In 1951, my family moved to a suburban neighbourhood not far from the creek. There were still a few farms and orchards around though by the mid 50's they were gone, converted to expanses of standard three-bedroom, yellow brick bungalows. The Mimico Creek was saved from the bulldozer by the fact that it was a flood plain.

For us boys, the creek was a fine place to play. It was close by, a short walk past various low, flat-topped factories to a line of trees that hid a narrow dirt path.

We did whatever we wanted. No supervision. No rules. We dug forts in the escarpment, swam naked, made camp fires, climbed the railway trestle and caught poison ivy. I spied on huge sleek fish, pike I guess, prowling through the shallows and cattails at the mouth. In the winter, we skated on it and occasionally fell through.

In the spring, it became a torrent, rapids replacing summer riffles. In late April fish briefly filled the swollen creek as they ran upriver from Lake Ontario. We used dip nets to fill bushel baskets with slim, silvery, five inch long smelts and a few big, fat, scary looking suckers. My mom cleaned, breaded and fried the smelt my dad and I caught.

As I got older and into high school my visits to the creek tailed off. But on one final visit, I'm guessing it was 1956, everything changed.

The colour of the creek bed was no longer grey shale with patches of green seaweed. It was transmuted to a bright yellow and rotting fish littered the banks. It was dead. Maybe I should have been angry, but I was just stunned. I went home and tried to forget but couldn't get it out of my mind and decided to look again the next day.

This time I walked upstream maybe a quarter of a mile along the wide plain on the east side of the creek until the yellow stopped. The west side was steep, a cliff maybe 20 or 30 feet high that ran down to the water. A thin yellow line of almost fluorescent liquid trickled down from the top, crawling over and around rock layers, finally marking where the die-off began.

Looking up, I could see the outline of a building and so I clawed my way to the top where I found a small pipe, an inch or so across, extending from the building to the edge of the drop-off. A poisonous effluent dripped from the end of the pipe and made its way to the creek below. The villain was a new metal plating factory, a consumer of dangerous chemicals, that defecated into the natural world.

I had no clue what to do. Pollution was common then and it would seem that the factory guys, whoever they were, knew best. I did nothing and question myself about it to this day.

When I recently googled the topic I found that there's still a huge amount of industrial pollution in that area, especially on the west side, south of the Queensway, where we lived. All kinds of heavy metals and chemicals have been found and remedial action has and is being taken although it seems that the volume of toxins outweighs our ability to deal with it. At least we aren't so forgiving now.

Now, there are better regulations and enforcement, and the poisoning of my youth is long gone. On a recent visit to Toronto I walked down to the creek at Jeff Healey Park (Woodford Park back then), and after making my way through some bush I sat on a rock for a while. I relived old memories and admired the simplicity of the scene, but also so amazing.

Next, I drove to its mouth on Lake Ontario, which is now flanked by Humber Bay Park with the requisite walkways, picnic tables and marinas. It's more controlled but still very attractive.

The fixers and improvers are still at it. I read there are plans to remove the concrete channels between Eglinton and Highway 401 to restore the natural water flow. Good.

We should all be grateful to the many caring and vigilant citizens and local government that brought the Mimico Creek back to life.