## 1 Introduction  
The \"GOLDFISH--Detection of Watercourse Contamination in Developing Countries using Sensor Networks\" project was an Information and Communication Technologies (ICT) project funded from 2012 to 2015 by the European Union (EU). It was developed by a consortium of \(11\) universities and organizations from Poland, France, Sweden, Croatia, Slovakia, Colombia, and Bolivia. The GOLDFISH project worked with the Raspberry Pi platform to integrate all its components and developed the sensors technology, the communication modules, the Central Management and Monitoring platform, and the communication algorithms. In the project's extension, an energy generation technology and a pollutant locator application were added [1]. The GOLDFISH project was designed, as can be seen in Figure 1, to sense river pollution with some embedded sensors, and to send these data to a Gateway (GW) on the river's shore. The GW sent sensor data to the central Management and Monitoring Station (MMS) via VPN through the Mobile network. The communication between the nodes in the river and between the nodes and the GW was achieved via WiFi (IEEE 802.11b) with a floating antenna incorporated in the sensor node design (see Figure 2). The GW had 2G/3G communication capabilities and it sent the sensor data through this channel. Once the MMS had the sensor data, it could show anomalies or alarms for higher than expected levels of pollutants. The system was tested in Europe and in Colombia. However, for tests in Colombia, the system had communication failures. The communication from the GW to the MMS did not work. There was a cellular antenna near the test site (it can be seen in Figure 2), but the data throughput varied between 20 and 95 kbps, and the data delay varied from 450 ms to 2.12 s to reach a server in Bogota D.C. (100 km from the test site). In addition, the VPN to the MMS had to be created with a server in Warsaw. After two days of testing, this communication part of the project (GW to MMS) did not work. These problems were probably due to the lack of availability of 3G channels at the test site and the high delays experienced in the 2G channel available. This might have caused the VPN request to expire before connecting with the MMS or before the data could be sent to the MMS. To solve the GOLDFISH project communication problem and to deal with even more restricted communication capabilities that can be present on more remote sites, we are proposing a Delay/Disruption Tolerant Network (DTN) that can use local transportation facilities to send and receive messages to Internet servers for non real-time and non-time-critical applications. The main idea is to send the sensor node information to the GW when possible or to a neighboring sensor node if it has a better probability to deliver the information to the GW. Sensor nodes (CLN) and the GW  
Figure 1: GOLDFISH project description. Sensor Nodes (CLN), Management and Monitoring Station (MMS), and Gateways (GW) are depicted. Figure 2: GOLDFISH project running in Colombia, 2015.  
will store all data until they can reach the next hop en route to their destination. For the GW, it will be a mobile node that will transport these data to an Internet connected site, where they will be sent to the MMS (See Figure 3). Sensor nodes can communicate with each other and with the GW and learn who are their neighbors, how often they meet, and calculate the delivery probabilities through other nodes, so they can make decisions about which node will be the next hop in their transmission. The GW will receive all messages from the sensor nodes and will wait until a mobile node (MAP) comes by and collects the data. These MAPs will be mechanical vehicles that will, eventually or periodically, visit the site and contact the GW. When the GW encounters a MAP it will calculate the MAP's delivery probability, and will decide if it gives the MAP all the data or if it should wait for the visit of another MAP with a better delivery probability.