Has anyone tried portable hydroelectric power devices?
They work like waterwheels with battery storage, pull behind boats and can also pick up wind. or hand-crank. Charges devices (and power banks), obviously waterproof.
I ran across this one -- expensive but compact 7" and user-friendly.
www.waterlilyturbine.com/
"WaterLily's rated output is 15W, but can generate as much power in 24 hours as expensive 100W solar panels. Generates up to 360 Watt hours of power in a day. A 14W solar panel will generate 42 Watt hours on a good day."
Others for half the price, bulkier.
Wait for it... someone saying, "Just make one yourself." ^_^ Instructions please, lol.