Which Apple Watch are you using?
Did you already to clean the openings for microphone and the speaker?
Some users also enabled/disabled the Water Lock a couple of times after cleaning the watch with warm water.
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If your Apple Watch has substances or debris visible in places such as the speaker ports, you can hold your Apple Watch under lightly running, warm, fresh water until it's clean. Soaps and other cleaning products shouldn’t be used. With Apple Watch Series 10, you can use a soft bristle brush to remove debris from the speaker ports.
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copied from: How to clean your Apple Watch - Apple Support