Our open-water group wants to swim despite a closure notice. How do I help change the plan?

The sign at the lake said the swimming area was closed because of water quality. One member looked across the clear surface and said, "That notice has probably been there for days. We can go in further along."

We had all arrived for a morning swim, and two people had driven an hour. I stayed out. I don't know whether the notice is old, and moving along the shore isn't an answer I can verify.

The [CDC's guidance for lakes, rivers, and oceans](https://www.cdc.gov/healthy-swimming/safety/how-to-safely-visit-oceans-lakes-and-rivers.html) says to check current advisories and closures, especially after heavy rain, and to stay out when signs say the swimming area is closed.

I offered to find the site's current update while we had coffee, but another swimmer said the group would never get anywhere if someone always found a concern. What would you say now, and what arrangement would help us check the venue before the next early drive? I want to help organise an alternative without having to prove that somebody would have become ill.