"Imagery shows water being discharged from August 25 to at least September 9; no water was observed on October 1, but it was detected again the next day," Yonhap News Agency quoted the website, 38 North as saying in its latest article.
The website also stressed although there were no other indicators, such as the emission of steam from the facilities, "intermittent discharge is not uncommon when the reactor is operating".
Earlier this week, 38 North also said satellite images suggested Pyongyang has been carrying out construction activities at the venue.
The suspicion comes in line with the International Atomic Energy Agency's report released in August, which suggested Pyongyang appears to have reactivated its 5-megawatt nuclear reactor at the complex, also judging by possible activities indicative of a discharge of cooling water.
The North previously re-processed spent fuel rods from the reactor to harvest plutonium for nuclear bombs.
Earlier this month, the North reopened its direct communication lines with the South, raising hopes for the resumption of stalled inter-Korean dialogue amid a drawn-out deadlock in denuclearization talks.
Last year, North Korea blew up a liaison office in its border town of Kaesong and unilaterally cut off all inter-Korean communication lines in anger over anti-Pyongyang leaflets sent from South Korea.