Dozens of people paddled down the Rio Grande in kayaks and canoes Saturday to protest a border fence they say will do little to stop illegal immigration but will destroy the impoverished region's burgeoning bird-watching industry.

On a one-acre site alongside a string of shrimp boats docked on the Brownsville ship channel stands a $2.2 million assembly of pipes, sheds, and humming machinery — Texas' entree into global efforts to make sea water suitable to drink.