Boating across Lake Lanier on a cloudless day, with the wind and sun in your face, thoughts of the lake’s chemistry might be as distant as the workweek ahead. That’s where Chattahoochee Riverkeeper cruises in on its pontoon boat, the Molly B. The Atlanta-based environmental watchdog group uses the craft — worn by weather and work — to monitor the lake, taking samples and testing them for chlorophyll-a, which indicates the level of potentially harmful algae growth. Algae’s growth season is April through October, with Chattahoochee Riverkeeper wrapping up its testing season on a cloudy, windy day last week.