One way to hold this word: think of a sponge that has taken in all the water it can hold. Nothing more will go in, so the extra water just sits there. The sponge is still a sponge, but it is heavy, soft, and it cannot do its job. Whatever waterlogged describes — a field, a boat, a pair of shoes — is in that state: full past its limit, and out of action because of it.
可以想成一塊已經吸到不能再吸的海綿。水再倒下去也進不去，只能留在表面。海綿還是海綿，但是變重、變軟，也擠不出用處了。waterlogged 形容的東西都停在這個狀態：吸飽了水，然後失去原本的功能。不管講的是操場、木頭，還是一艘船，畫面都一樣——不是「濕」，是「滿到不能用」。
From the word’s history
The packet source gives only: waterlogged is waterlog plus -ed, so it names the state of having had water let in.
來源資料只說 waterlogged 是 waterlog 加上 -ed，也就是「被灌進水」的狀態。這條線索雖然簡單，方向卻和現在的用法一致：重點一直是水進到裡面去，不是表面淋濕。
Wiktionary etymology supplied in this packet: From waterlog + -ed.
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