It's the gravitational pull of the moon on the sea

When there is a full moon the whole of the moon is pulling the water so BIG tides, spring tides.
When there is not a full moon only part of the moon is pulling sea, so not such big tides. At this stage the moon looks about the size of a Swede, so called neeps.

or maybe not

Posted By: Claygate_Canary, Oct 29, 15:56:46