Stroll across the Brooklyn Bridge at night, peer down, and you might see a network of lights floating on the East River, like some wayward school of tropical fish. The lights serve more than an aesthetic purpose: They inform passersby about the state of the river’s health. River Glow—a project by architectural firm The Living and Eric Forman—uses solar panels to power a pH sensor, which triggers the lights to shift from green to red when the acidity of the water rises (when, for example, the river absorbs excess carbon emissions from the air).

The result, says The Living's David Benjamin, "is a cloud of light that hovers above the water's surface." From the vantage of the bridge, it is a perversely beautiful sight and, to the intrepid swimmer, a cause for not a small measure of doubt.