The New York Times –  A stir-crazy nation wonders: Is it safe to stroll on the beach in a deadly pandemic? How about a picnic in the park? Or coffee with a friend at an outdoor table? The risk is in the details. “…“The virus load is important,” said Eugene Chudnovsky, a physicist at Lehman College and the City University of New York’s Graduate Center. “A single virus will not make anyone sick; it will be immediately destroyed by the immune system. The belief is that one needs a few hundred to a few thousand of SARS-CoV-2 viruses to overwhelm the immune response.” While the risk of outdoor transmission is low, it can happen. In one study of more than 7,300 cases in China, just one was connected to outdoor transmission. In that case, a 27-year-old man had a conversation outdoors with a traveler who had just returned from Wuhan. Seven days later, he had his first symptoms of Covid-19. “The risk is lower outdoors, but it’s not zero,” said Shan Soe-Lin, a lecturer at the Yale Jackson Institute for Global Affairs. “And I think the risk is higher if you have two people who are stationary next to each other for a long time, like on a beach blanket, rather than people who are walking and passing each other.”

“In my opinion, pool water, fresh water in a lake or river, or seawater exposure would be extremely low transmission risk even without dilution (which would reduce risk further),” Dr. Rasmussen said in an email. “Probably the biggest risk for summer water recreation is crowds — a crowded pool locker room, dock or beach, especially if coupled with limited physical distancing or prolonged proximity to others. The most concentrated sources of virus in such an environment will be the people hanging out at the pool, not the pool itself.”..