A wellbore fluid monitoring system includes a housing, a first sealing element, a second sealing element and a sealing unit. The housing is configured to be securely disposed in a portion of an annulus within a bell nipple below a rotary table of a wellbore drilling assembly. The annulus is formed by a drill string of the wellbore drilling assembly and an inner wall of a wellbore being drilled by the wellbore drilling assembly. The housing includes a first open end and a second open end. The housing is configured to house an air flow sensor disposed within the housing. The first sealing element is attached to the first open end of the housing. The first sealing element is configured to seal and unseal the first open end. The second sealing element is attached to the second open end of the housing. The second sealing element is configured to seal and unseal the second open end. The sealing unit is disposed in the portion of the annulus. The sealing unit is connected to the housing, the first sealing element and the second sealing element. The sealing unit is configured to actuate the first sealing element and the second sealing element to seal or unseal the first open end and the second open end, respectively, based on a liquid level in the portion of the annulus.