A whistle is so effective, so cheap, and so small and easy to keep on you. I was rescuing a couple boats and paddles and got far downstream from the swimmers. I had to hike back up the bank and to the road and through some private property with the permission of the land owners (the bank was impassable along the river and the current to fast along the steep bank to paddle upstream). I used the whistle to get the attention of the property owner so that I would not surprise them at close proximity - this was effective. I explained later my intent for using the whistle and they very much appreciated it. I continued using the whistle periodically to let the swimmers who were long out of sight know my location and that I was making my way back to them. They did not have a whistle but the used their fingers to whistle loud back and let me know the same. 2 rescued boats and one out of 2 rescued paddles later, we were able to find each other after getting separated rather quickly.

No - I don't know whistle signals. To be honest so few people have whistles I don't think it helps if you are the only one who knows whistle signals and nobody else. You know? But I agree that a crew that uses a set of whistle signals effectively certainly is a solid idea. Getting the attention of crew earlier via whistle (as opposed to shouting or whatever) can make such a difference especially in a swim with gear lost/compromised or an entrapment situation - as sometimes just a short distance in a swift section of river with steep impassable banks can make for so much time added to get to the upstream person.

Just reading through this thread it seems like there's a huge range of types of whistle blasts that people interpret various ways and the only consistent variable is that people agree that people are used to interpreting different things. I agree with a few people from earlier on that having one long blast for trouble keeps it simpler than wondering if two short blasts meant trouble upstream or three short blasts meant trouble downstream, etc.  But I can't say I make a practice of checking with whatever crew I'm putting on with what they are used to as far as whistle signals, which would be a great idea. Sounds like a good job on the clean-up Matt by the way. :)

There is definitely more than one way to utilize a whistle, this forum topic is a great example of that!

After reading all the posts, I discovered I typically go with one blast for attention and then repeated whistle blows for help or an emergency. I have used/heard a good short loud blast to indicate a swimmer also (attention!). The upstream and downstream whistle signal options may get confusing and not everyone knows the specifics.

I don't use my whistle for basic communication on the river (but I'm also not paddling g5 where I may not be able to visualize my boating partners), This is where the hand and paddle signals come into play for communication.

Whistles used in excess are annoying and lose their "attention" grabbing factor.

BTW Haverly, I didn't dish the negatives your way, must be another friend of yours!