In this paper, we experimentally demonstrate a cost-efficient real-time field programmable gate array (FPGA)-based system for underwater optical wireless communication (UOWC) at a data rate up to 25 Mb/s over a 10 m underwater channel. The transmitter of the system employs a commercial blue LED as a modulation light source and an FPGA unit for transmitter baseband signal processing, and an avalanche photo diode cascaded with an FPGA unit for receiver baseband signal processing at the receiver side. We also suggest a simplified system model to characterize underwater optical link. Three types of hard-decision forward error correction codes are introduced to investigate the impact on the receiver sensitivity in long distance transmission cases. By adding additional link attenuation, we experimentally measure the attenuation coefficients for different water conditions. Based on the measured results, the achievable link distance for clear ocean water is estimated up to 118 m at the transmitted electrical power of 30 dBm. The proposed UOWC system takes both implementation complexity and cost into consideration and also provides a significant guidance to the future real-time high-speed underwater optical communications.