The fluctuation of seawater is caused by the tidal force produced by the moon and the earth. Because the earth and the moon are in constant motion, and the relative positions of the earth, the moon and the sun are changing periodically, the tidal force is also changing periodically, which makes the tidal phenomenon happen periodically.

The moon is attractive to the earth's seawater, and the distances between the points on the earth's surface and the moon are different. The place facing the moon is attracted by gravity, and the seawater expands outward, while the place facing the moon is attracted by gravity, and the centrifugal force becomes larger. Under the action of centrifugal force, the seawater expands to the place facing the moon, and there will also be a high tide.

Extended data:

Precautions:

According to the time difference analysis of the average tide, the daily range of 40 is divided into spring tide period and the daily range of 50 is divided into low tide period. The dry conditions of spring tide and neap tide are very different. When the spring tide recedes to the lowest water level, some parts of the seaside (including reefs) can bottom out or emerge from the sea. Small tides don't bottom out and expose coral reefs. This kind of water fisherman must master it carefully.

For example, estuaries with domestic garbage, eddies at high tide, backwaters and deep pools and reefs at low water are all places where fish like to gather. It is difficult to find fishing in these special water conditions. There is also a kind of water situation, that is, at dawn and dusk, as long as the tide begins to rise, the water in the sea is slightly dynamic and all kinds of fish are more active. It is the golden time for sea fishing, and it is also a kind of water situation that is difficult to find.

Baidu encyclopedia-rising tide