Objective To investigate the gross α and gross β radioactivity in Dongjiang River during high and low flow periods in Dongguan City, China, and evaluate the radiation safety status of Dongjiang River as a source of drinking water. Methods The gross α and gross β radioactivity levels were measured in the source water, treated water, and tap water from eight water treatment plants along the Dongjiang River, which relied on Dongjiang River water as their source, during both high and low flow periods. The annual internal effective dose from consuming Dongjiang River water was estimated. Results In high flow period, the gross α and gross β radioactivity levels were 0.016-0.041 and 0.063-0.140 Bq/L for source water, 0.011-0.039 and 0.064-0.131 Bq/L for treated water, and 0.013-0.024 and 0.078-0.127 Bq/L for tap water. In low flow period, the gross α and gross β radioactivity levels were 0.012-0.029 and 0.055-0.141 Bq/L for source water, 0.012-0.019 and 0.054-0.124 Bq/L for treated water, and 0.012-0.024 and 0.083-0.134 Bq/L for tap water. The estimated total effective doses of gross α and gross β radioactivity caused by consumption of water from Dongjiang River were 3.6 and 0.48 μSv/a, respectively. Conclusion The gross α and gross β radioactivity levels of water from Dongjiang River in Dongguan City are below the radioactive indicator values specified in the Standards for Drinking Water Quality (GB 5749-2022), remaining within the range of natural environmental background. The annual internal effective dose caused by consumption of water from Dongjiang River is below the individual dose limit set in the Guidelines for Drinking Water Quality.