Environmental and water quality monitoring are of utmost interest in a context where land use changes, uncontrolled agricultural practices, human settlements, tourism and other activities affect a watershed and condition the usage of their surface waters. Such is the case of Mar Menor lagoon in Southeast of Spain, where the EU H2020 SMARTLAGOON project stands and is implementing an intelligent environmental infrastructure and modelling that will let the construction of a digital twin of the lagoon. Performing environmental monitoring is expensive and the number of sampling locations is typically limited by the budget. For this reason, we have developed a low-cost monitoring system that can be integrated in a small-sized buoy and attached to fishing and recreational boats allowing citizens to gather water quality information - i.e. electrical conductivity and temperature - with the use of their smartphones. The usage of such devices leads to key stakeholder engagement and citizen science activities that could enrich and ease the data gathering process. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).