This study investigated the toxicity of heavy metals such as Cu, Fe, Cr, Zn and Mn and the influence of water quality in Garang Watershed Semarang (Banjir Kanal Barat River), Central Java Indonesia for enhancing fisheries food security. The fish biomarker in this research is Nile Tilapia (Oreochromis niloticus). The range of Cu, Fe, Cr, Zn and Mn in aquatic environment were 0,15 mg/L; 0,82 mg/L; 0,025 mg/L; 0,562 mg/L and 0,01mg/L. The range of Cu, Fe, Cr, Zn and Mn in Nile Tilapia were 2,547 mg/kg; 306,3 mg/kg; 0,36 mg/kg; 16,69 mg/kg and 35,6 mg/kg. Toxicity in fish is exceeded the limits of food security regulation in WHO and BPOM, and water quality regulation in Government Regulation of Indonesia No 82/2001 on Water Quality And Water Pollution Management. Management in water quality is and toxicity is important for enhancing fisheries food security. Maintaining food security in the fishery sector is very important for the stability of community nutrition because with good food public health will be guaranteed.

Phytoplankton can be used as an indicator for water environment quality in the watershed area. This research was conducted in Garang Watershed, Central Java, Indonesia. The aims of this research are to study the environmental assessment of Garang Watershed Central Java, Indonesia using phytoplankton diversity and their relationship to water quality. Sampling location was determined based on the Governor Regulation of Central Java Provincial No. 156/2010 about the segmentation of Garang Watershed. Plankton Net No.25 was used for collecting phytoplankton in Garang Watershed. Phytoplankton density ranged from 13 to 53 ind/L. The number of species in the range of 4-8. Diversity index in the range 1.07-2.06. The result of diversity index shown that this rivers is lightly polluted. Phytoplankton stabilization was moderate while phytoplankton evenness was spread. Water quality index in this research are: Phosphate, Nitrate, Nitrite, Ammonia and Fe.

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Abstract. Banjir Kanal Barat is a river in the Garang watershed, Semarang City, Central Java, Indonesia. Its function is as a source of water for the community. The level of pollution in this river is already high. The purpose of this study is to provide advice to governments, communities and related stakeholders to realize integrated river management, and fisheries-based food security is achieved. This research method is: analyzing the water quality of the Banjir Kanal Barat river, and analyzing the amount of faecal and total coliform bacteria content in the Banjir Kanal Barat river, and analyzing how to overcome the decline in the quality of waters of the Banjir Kanal Barat river due to faecal and total coliform bacteria pollution. The results showed that the water quality at the research location was still in the quality standard. The content of coliform dan faecal bacteria at the study site exceeds the quality standard, this is due to the influence of domestic waste from households. The thing that needs to be done is counseling the existence of a clean and healthy life, especially for people who are still throwing domestic waste into the river. The existence of water purification equipment is also very necessary to overcome this problem. Water quality management can be done with policy analysis. Regulations related to water quality management can be analyzed and then given solutions and recommendations related to these rules so that policies can be taken that are sustainable, integrated, and coordinated between various parties in managing river water quality and food security. Keywords: food security, water quality, river, faecal coliform, total coliform

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