We studied patterns in organic carbon pools and their origin in the Tana River Basin (Kenya), in February 2008 (dry season), September-November 2009 (wet season), and June-July 2010 (end of wet season), and covering the full continuum from headwater streams to lowland mainstream sites. A consistent downstream increase in total suspended matter (TSM, 0.6 to 7058 mg l?1) and particulate organic carbon (POC, 0.23 to 119.8 mg l?1) was observed during all three sampling campaigns, particularly pronounced below 1000 m above sea level, indicating that most particulate matter exported towards the coastal zone originated from the mid and low altitude zones rather than from headwater regions. This indicates that the cascade of hydroelectrical reservoirs act as an extremely efficient particle trap. The decrease in 7Be/210Pbxs ratios of TSM downstream (range: 0.43 to 1.93) during the wet season indicated that the increasing sediment load in the lower Tana was largely due to recent surface erosion. During lower flow conditions, however, the gradual longitudinal increase in TSM coincided was more variable 7Be/210Pbxs ratios (0 to 4.5), suggesting that bank erosion and/or remobilisation of older sediments are the sources of the increasing TSM concentrations downstream. With the exception of reservoir waters, POC was predominantly of terrestrial origin as indicated by generally high POC/Chl-a ratios (up to ? 41 000). Stable isotope signatures of POC (?13CPOC) ranged between -32 and -20 ¿ and increased downstream, reflecting an increasing contribution of C4-derived carbon in combination with an expected shift in ?13C for C3 vegetation towards the more semi-arid lowlands. Sediments from the main reservoir (Masinga) showed ?13C values higher (-19.5 to -15.7 ¿ than found in any of the riverine samples, indicating selective retention of particles associated with C4 fraction. Dissolved organic carbon (DOC) concentrations were highest during the end of wet season (2.1 to 6.9 mg l?1), with