Trenches are constructed for water distribution, providing natural habitat and ease to harvest of fish in the agricultural field of paddy cum fish cultivation. Owing to water in the field, trenches get filled with sludge, which restricts flow of water and fish movement. Therefore, the repair and maintenance of the trench is required and is performed manually by hands in four steps by: digging the sludge, lifting a handful of sludge, piling the sludge near the trench, and leveling the side walls. Each step involves ergonomic challenges to the workers especially awkward postures, twisting of back and repetitive strain. The aim of the study is to measure working posture and back-compressive force (BCF) of the workers during repair and maintenance of trenches and also to provide an intervention to improve working posture and BCF for increased comfort and safety of the workers. Kinovea software was used to analyze the posture of the workers using still photographs and videos. Two manikins were created for the 5th and 95th percentiles northeast Indian female worker using Dassault CATIA software to determine RULA score and BCF. The REBA analysis was performed. The overall RULA and REBA scores for both percentiles population were 7 and 13, respectively. The BCF on the L4-L5 lumber spine was 3646 N for the 95th percentile, which exceeded the allowable NIOSH Action Limit. In order to improve working posture and reduce BCF, a multi-functional trench digger was designed and used. The use of trench digger improved the RULA and REBA score. The BCF was reduced to 1549 N for 95th percentile workers.