The present invention concerns an elongated capacitive sensor (1) for fluid monitoring. The sensor (1) comprising: a fibre support (5) made of a dielectric material or dielectric composite material; and a first electrode (7, 9) and a second electrode (7, 9) arranged longitudinally along the fibre support (5), the first and second 5 electrodes forming together with the fibre support (5) a capacitive sensing element whose capacitance is dependent upon one or more electrical properties of one or more materials inside the support (5) and/or outside the support (5), and/or is dependent upon a change of materials configuration and associated overall change of one or more electrical properties inside the support (5) and/or outside the support (5).