Owing to its relatively low absorption loss and high data transmission rate, wireless blue light communication is becoming an increasingly attractive technology for underwater applications. Here, we demonstrate an underwater optical wireless communication (UOWC) system that communicates using blue light-emitting diodes (LEDs) with a dominant wavelength of 455 nm. Under the on-off keying modulation scheme, the waterproof UOWC system achieves a bidirectional communication rate of 4 Mbps based on the transmission control protocol (TCP) and exhibits real-time full-duplex video communication with a transmission distance of 12 m in a swimming pool, offering great potential for practical use in real-world scenarios, such as carried around or attached to an autonomous vehicle.