KUSHIRO, Japan — In the early 1980s, engineers straightened out stretches of the Kushiro River, which had meandered some 100 miles under Hokkaido’s big sky here in northern Japan, flowing through green hill country and rural towns, winding through the nation’s largest wetland and this port city’s downtown before emptying into the Pacific Ocean.

Later in November, work is to start again. But this time bulldozers will be moving earth to put curves back in a stretch of the river that had been straightened out, restoring its original, sinuous, shape.

For decades, Japan pursued economic development at all costs, but it is now emphasizing the importance of protecting the environment. So under a 2003 law that aims to reverse decades of destruction, the Kushiro River will be the first of perhaps many straightened rivers to regain some of its original curves.

Still, in a country famous for heedlessly paving rural areas in concrete to create jobs and to buttress the half-century rule of the Liberal Democratic Party, some environmentalists and local residents are skeptical of the new projects. With no rivers left to straighten, they say, the authorities nowadays are simply starting to curve them instead. Can politicians and bureaucrats be trusted to repair nature?