When should I stay off the water because of weather or conditions?

USRowing's Safety Guidelines recommend not launching when:

• Lightning or thunder: you see lightning, hear thunder or see skies darkening fast. If you're already out, head for the nearest shore immediately. If the storm reaches you, land, get out of the boat and wait. Don't handle boats or riggers, or load a trailer, during the storm.
• Fog: visibility is under 100 yards. If fog rolls in while you're out, slow down, sound a horn or whistle, and follow the shore back.
• High wind or rough water: waves or wind make the boat hard to steer or likely to swamp. If wind comes up suddenly, go back if it's safe, or land and wait.
• Darkness: you don't have proper lights. Boats need a red light to port and a green light to starboard at the bow, plus a white stern light, and should row only on familiar water.
• Tides and currents: tidal conditions are extreme.

Cold: hypothermia is a risk when water is below 80°F and very dangerous below 50°F. When the air is below 40°F or the water is below 50°F, a launch should stay within 100 yards of every shell. Some clubs stop all rowing in those conditions.

Heat: hydrate before and during the row, avoid midday sessions, wear light moisture-wicking clothing, a hat and sunscreen. Train early or late when temperatures above 90°F are expected.

Clubs set their own limits for their waterway on top of these, and they can be stricter.