What semantic notions underlie 氵(left radcial for water) with 沮 (to prevent; to ruin; disheartened)? Is weeping the underlying semantic notion? Doubtless weeping involves water (tears), and usually follows gloom.   Unusually CUHK blazons no etymology. Yellowbridge.
汉字源流字典 (first picture) says its original meaning was muddy wetland.
王力古漢語字典 (second picture) also lists this meaning (but does not explicitly say whether it's the original meaning). There is also an example sentence where both 阻 and 沮 are used: 不知山林险阻沮泽之形也，不能行军。My understanding is that 阻 and 沮 are very similar but not exactly the same, with 沮 being water-related obstacles (swamps) and 阻 being mountain-related obstacles (the radical 阝 is usually related to hill or mountain).