For the last decade, scholars have studied how infrastructure produces and reworks waterscapes, impacts material flows and resources access. In this paper, we analyze waterscapes as cyborgs: ontologically uncertain entities, embedding living things and machines, social reality and chimera, that shape asymmetries in the social world, that have agency and towards which humans become obliged to whether they like it or not. We discuss a specific technical artefact: metrics and modeling. We analyze the knowledge and ignorance they produce, their political effects and the manner water resists quantification. The analysis is based on an amphibious case, the brackish marshes (marismas) of the Guadalquivir estuary in Southwestern Spain. For centuries, their values, uses and appropriations have been subject to intense conflicts producing boundaries between land and water, contested by unexpected “outflows”. Today, such a cyborg embeds heavy hydraulic infrastructure, irrigated rice production, a protected area (Doñana), migrating birds, navigating boats and sediments between the harbor of Seville and the ocean... These are governed by a complex system of devices to measure and model water and salt. Such a system actively frames access to water and land for farmers as well as for animals. At first sight, it appears to have two contradictory characteristics. On the one hand, it seems greatly sophisticated, it produces figures that “count”, circulate and shape governing devices and actors’ practices. On the other, it also embeds significant ignorance and uncertainties. We propose to analyze how, instead, these two characteristics work together and how knowledge and ignorance cooperate politically.