I work at technical support and I heard a story about a customer that lost his internet connection when there was a high tide. I do not know the details but is it possible that high tide can affect wireless internet signals?
This is absolutely not true. I run a WISP and we shoot over the water to islands from 2 miles to 16 miles. Those customers suffer from tidal related Multipath issues.
Think of the water as a sheet of reflective glass. As the glass moves up and down (tidal) the radio signal bounces off the reflective material. At times, at just the right angle, the reflected radio wave can cause havoc with the primary radio wave reaching both the radio on your end and that of the sending radio. This will happen not at high or low tide, but when the angle is just right.
Now consider that the water is not a flat piece of glass, but a continuously changing surface with ripples and waves. Those ripples change when the "Angle is just right".
The only solution we have found is to get the radio up in the air as high as possible. Tree? Somewhere. And to "hide" the water from the radio. However, radio waves do penetrate structures.