I ordered one of these a week ago, arrived today.
It's loud, like uncomfortably loud if you're next to it when it's cranked. I turned the one speaker up and walked 1/4 mile away and could still hear it pretty clearly. Bass isn't ground shaking, but it gets the job done.
Think I may order another so I can have the stereo effect. It's not weather "proof" but weather resistant.
I was going to install in-ground subs and wire up speakers around the pool. This is a cheaper, easier, and more portable solution. It will definitely be loud enough for what you're looking to do, plus you could also use it in the shop or house or wherever else. They also have a 100 day return policy if you're not satisfied and they cover the shipping, so if you're not happy just send it back.
The Loudest Bluetooth Performance Speaker | SOUNDBOKS