Since mid-May, some 20,000 nine to 12-year-olds in Atlantic Canada, Quebec and the US states of Maine and Connecticut have stood on the shores of lakes, ponds and rivers or balanced on rocks. Their mission? To release salmon and trout fry into the water, some waving the small fish an emotional goodbye.
The young "fish wardens" have been taking part in a scheme called Fish Friends, set up by Canada's Atlantic Salmon Federation. It began in 1992 with 29 schools and now involves more than 700, making it one of North America's most successful environmental education programmes. Pupils spend four months raising millions of fry, then release them.
Lewis Hinks, the federation's regional director for Nova Scotia, said: "We were looking for a way to get the youth interested in Atlantic salmon and cold-water fisheries, which are important to our economy and are a sign of the health of the local environment. We also wanted to give the kids a hands-on way to learn biology and ecology, and to learn what mistakes, such as overfishing, we have made."
By a happy coincidence arranged by Mother Nature, the fry reach the point at which they can be released just at the time when the irresistible urge to muck about in mud hits young Canadians.
"Some kids don't need any prompting to run into the water and release the fry," Mr Hinks said. "Others are less exuberant and stand on the rocks. Sometimes the kids are lucky enough to see the fry they've raised mixing with wild fish. They wave goodbye with mixed emotions, wishing the fry luck and a safe journey."
The 224-page Fish Friends teacher's manual is not likely to challenge Izaak Walton's book The Compleat Angler, which has been in print since 1653. But it is stuffed to the gills (pun intended) with lesson plans that use fish, as well as information on their life cycles, habitat and the effects of pollution upon them.
One lesson shows how to read a fish's scale (like the rings of a tree); another teaches pupils how to draw a graph illustrating the collapse of a fishery on the Adanac River since 1940; and another shows how long-term economic sustainability rests upon environmental and biological sustainability - a hot issue on Canada's Atlantic coast since the closure of the cod fishery more than a decade ago.
Each school needs its own 125-litre aquarium, chiller unit, filter and oxygenator, which cost about $1,500 (Pounds 800). In Newfoundland, these costs are covered by Newfoundland Power, while in Nova Scotia they are paid for by the schools themselves or by local voluntary fundraisers.
"The kids learn extremely valuable lessons," Mr Hinks said. "On a day-to- day basis, they look after the tank, monitor the water's temperature and use that information to predict when eggs will hatch. They are responsible for identifying and removing dead eggs from the tank and for ensuring that filtration systems are clean and working properly."
Mr Hinks said one of their proudest moments occurred when a son gave his father "what for" after he dropped a cigarette butt into the river where the child had released fry. The boy told his father to pick it up and "stop polluting my fish's river".