Colorectal cancer (CRC) is the fourth most commonly diagnosed cancer in the world and the third in France. Its incidence is steadily rising in developing nations. Anastomotic leak (AL) is a major problem in colorectal surgery affecting at least 7% of patients operated on for left colonic cancer. It is the most feared complication after colorectal anastomosis, associated with mortality, prolonged hospitalization, impaired health related quality of life (HRQoL) and increased health care costs. Intraoperative fluorescence angiography (IOFA) with indocyanine green (ICG) may help preventing AL. Available studies on the effects of IOFA with ICG are heterogeneous and randomized controlled trial are scarce. Our aim is to demonstrate that IOFA with ICG could lead to a reduction of AL rate after left-sided or low anterior resection with anastomosis for CRC. The FLUOCOL-1 study is the first national, multicenter, single blind, randomized, 2-arm, phase III superiority clinical trial. The primary endpoint is the occurrence of an AL 90 days post-operation. AL is defined as any anastomotic dehiscence with leakage into the pelvic cavity diagnosed upon imaging or at surgical exploration or any isolated pelvic organ-space infection with no evidence of fistula as defined by the International Study Group of Rectal Cancer. The study population will be made of adult patients with left-sided or high rectal cancer scheduled to undergo elective left colectomy or high rectal resection (by open, laparoscopy or robotic surgery) and with expected stapled or hand-sewn intraperitoneal anastomosis. The exclusion criteria are mainly an emergent surgery; rectal cancer requiring total mesorectal excision and anastomosis expected below the peritoneal reflection; CRC requiring total or subtotal colectomy; CRC requiring transverse colectomy; recurrent CRC and locally advanced colorectal cancer requiring multi-visceral excision. A total of 1010 patients will be necessary (39 patients in each centre during 36 months). An interim analysis for efficacy and futility is scheduled when half of the participants will have been recruited. In case of positive results favoring IOFA, this study would define the use of IOFA as a standard of care in colorectal surgery. At the patient level, a significantly lower rate of AL will reduce hospital stay and stoma rate, and will ensure improved postoperative recovery, faster return to normal activity and better long-term oncologic outcomes.