The world's climate change has an impact on the hydrological cycle which disrupts the water supply of irrigation systems. Water resource management is the key to solutions, especially in the agricultural sector. Therefore, efficient management of water resources in all irrigation areas (DI) must be carried out. Integrated Water Resources Management (IWRM) is a participatory watershed management concept that is expected to increase the carrying capacity of the watershed so that it continues to be sustainable [1]. The irrigation network is one of the management components in IWRM that involves the role of farmer organizations including Perkumpulan Petani Pemakai Air (P3A), Gabungan Perkumpulan Petani Pemakai Air (GP3A) dan Induk Perkumpulan Petani Pemakai Air (IP3A) [2]. The management of water resources involves many stakeholders with a large area having main problems with water distribution in the dry season due to distribution problems that lead to conflicts. The purpose of this paper is to examine the role of farmer organizations in irrigation network operational activities for the sustainability of IWRM management in the Colo Fixed-Weir which consists of 12 DI and is divided into West Colo consists of Klaten, Wonogiri, and Sukoharjo areas, and East Colo consists of Sukoharjo, Karangnyar, Sragen, and Ngawi. The focus of this research is on irrigation management under GP3A Karanganyar with an area of 119 Ha, consisting of 16 villages that received awards. Data were collected in the form of legal documents that regulate institutional and organizational performance in Colo Fixed-Weir. Focus Group Discussion (FGD) was conducted on GP3A and management apparatus in Karanganyar. Deep-interview with the head of GP3A was conducted also. Data were analyzed to find the performance of GP3A and P3A who can manage water resources in DI according to their needs while carrying out their functions and roles under policy regulations. The conclusion is that the key success factors are trusted leadership and the presence of local wisdom in the farming community. And the operational rules are technical, measurable, and scheduled in the agreement, which can be managed flexibly according to the situation of the farmers' needs. This can be done because between them there is mutual trust and a sense of responsibility for the common interest.