Waterproof Ultrasonic Proximity Sensor JSN-SR04T
If you need an industrial-grade, waterproof integrated ultrasonic distant sensor, this unit from PMD Way is for you.
Unlike the cheaper HCSR04 modules, this system has a separate controller board with a 2.5m lead that ends with the waterproof sensor - so you can get the sensor wet and keep the electronics safely away from the elements.
The sensor can measure distances between 20 and 600cm with an accuracy of up to 2mm. The output from the sensor can be determined by measuring ping times as with other sensors - or, unlike cheaper units - you can choose from TTL serial data output.