The tide was at its highest.

潮水那时正处于最高位。

《柯林斯英汉双解大词典》

The secret of success is to develop the habit of doing quickly, to take advantage of the tide rise the highest moment, not only there is no resistance, but also can help you quickly succeed.

成功的秘诀，是在养成迅速去做的习惯，要趁着潮水涨得最高的一刹那，不但没有阻力，而且能帮助你迅速地成功。

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Low water mark: the highest reach of the water at low tide.

UNESCO: L O S S A R Y

High water mark: the highest reach of the water at high tide.

UNESCO: L O S S A R Y

Late this morning was high tide along much of the coast, and the highest water levels of Isaac are likely being experienced at many locations.

FORBES: Hurricane Isaac and New Orleans: It's All About Water