As the Syrian conflict intensifies, thousands of refugees fleeing the violence have been making the clandestine journey assisted by a network of Syrian and Turkish activists and smugglers across the Orontes River that separates northern Syria from southern Turkey.

Each night, across this river and all along the border, new secrets of the bloodshed in Syria arrive. Rickety wooden boats ferry a stream of people, some walking and some wounded, to the safety of Turkey, on a flight from cities and villages racked by fighting.

As the pace of the government assault has quickened in recent days, so...