From Longman Dictionary of Contemporary Englishhigh waterˌhigh ˈwater noun [uncountable] TTWDNthe period of time during which the water in a river or the sea is at its highest level because of the tide OPP low water → come hell or high water at hell1(22)
Examples from the Corpus
high water• The photographs were taken at a high water level.• As to oil I use the lightest possible, which is grapeseed oil, but it has a high water content.• There would be no more high water.• They said high water levels in the Sacramento delta, which spills into the San Francisco Bay, were also worrisome.• But it was a misreading to suppose that the vote then marked the high water mark on the issue. 