## 1 Introduction  
The development, sustainability and business competitiveness of Portuguese agriculture are highly dependent on irrigation [1]. In turn, global changes lead to a decline in available water resources [2], implying that water saving is strategic for the development of agriculture. The management of hydro-agricultural perimeters with river gravity-based supply has specific characteristics, especially if the drainage water is reused to mitigate water scarcity and improve the water distribution, as is the case of the Lis Valley Irrigation District (LVID). This practice raises concerns regarding farmer and consumer safety. It is therefore important to monitor the microbiological quality of water to obtain information for its rational management, reduce environmental and public health risks, and support farmers in the adoption of more appropriate practices; in short, to contribute to the sustainability of irrigated agriculture [3].  
Fecal coliforms, e.g., _Escherichia coli_, mainly found in the intestine of human beings and warm-blooded animals, are used as indicators of the water microbiological quality. These bacteria, indicating fecal contamination, and thus the putative presence of pathogenic microorganisms, are highly relevant in medical microbiology, due to the water-carrieddiseases (sanitation conditions and drinking water quality), as well as in the assessment of environmental impacts caused by anthropological action. As surface and subterranean water resources can be affected by various activities developed in the hydrographic basins, it is important to study the quality of the water entering a system and returned to the aquifer after use. There is also an emergent global health concern regarding antibiotic (AB) resistances, involving the transfer of bacteria and genes between humans, animals and the environment. The transmission events of widespread AB resistant strains are common [4]; therefore, quantifying the pathways and identifying the sinks and bottlenecks for environmental transmission are fundamental to manage the global AB resistance crisis [5].  
Rice cultivation has a very important economic and social value in Portugal; rice is a strategic crop for food security in some countries, and consumption throughout the Mediterranean is increasing steadily. Traditionally, rice is grown in level basins and irrigated by continuous flooding, requiring a higher irrigation allocation than most crops, thus implying greater pressure on water resources [6]. On the other hand, paddies allow high productivity in soils with very poor drainage and high risk of salinity. These facts explain the need to save water in rice production and to safeguard the environmental sustainability of rice-growing agroecosystems, to ensure the viability of this crop; this topic concerns farmers and political authorities, and therefore is the object of study and experimental development [7].  
Considering the growing concerns about pollution of surface and ground waters in general, the knowledge of the environmental impacts of rice production on the ecosystem is relevant for its sustainability. However, there are scarce studies on the microbiological impacts of rice fields in Portugal, especially considering that information is required at the level of each rice-growing ecosystem. Contributing to a greater knowledge on the subject, the objective of this study was to determine the impact of rice farming activity, at the small watershed scale in a Mediterranean area, on the microbiological quality of superficial water. This information, available for water management organizations, will support measures to improve and minimize the risks regarding the conservation of surface and groundwater bodies. This work took place under the scope of the Lis Valley Water Management Operational Group [8] and the MEDWATERICE Project [9].