The River Tisza is one of Central Europe's most important rivers. In the last one and a half century numerous anthropogenic activities have influenced its watershed. As a result measures need to be taken to protect its water quality, necessitating a comprehensive picture of the spatial and temporal variability of its processes, which this study aims to extend further. In this study five sampling locations were analyzed in the upper section of the Tisza over the time interval 1974–2005, dealing with 24 parameters using multi-variate data analysis methods. Employing time series analysis and taking the river's tributaries into account, the strong influence of the River Szamos was pointed out, while stochastic connections indicated the influence of the Tiszalök Water Barrage System on the spatial variation of the Tisza's processes. Finally, by using principal component analysis (PCA), the different background factors were revealed in space and time (seasonal separation) as well. During summer the processes tended to be nitrogen-related, while during winter inorganic compounds play a greater role. Most importantly, spatial variety was observable in the factors. Key words: data analysis, principal component analysis, River Szamos, River Tisza, stochastic connections, Tiszalök Water Barrage System (WBS), water quality Introduction The River Tisza collects the waters of the Carpathian Basin's eastern region. According to Lászlóffy (1982), the area of its watershed is 157,186 km 2 . Less than one third of it is located in Hungary (Fig. 1). From its source in the range of the Maramorosszkiy Massiv (in Hungarian: Máramarosi-havasok) to its confluence with the Danube, it stretches for 966 km Addresses: *Corresponding author, address: H-1117 Budapest, Pázmány P . stny. 1/c, Hungary e-mail: tanospeter@gmail.com Received: August 28, 2010; accepted: December 22, 2011 1788-2281/$ 20.00 © 2011 Akadémiai Kiadó, Budapest Central European Geology, Vol. 54/4, pp. 345–356 (2011) DOI: 10.1556/CEuGeol.54.2011.4.3 Exploratory data analysis on the Upper-Tisza section using single and multi-variate data analysis methods Péter Tanos*, József Kovács Ilona Kovácsné Székely Department of Physical and Applied Geology Institute of Methodology Eötvös Loránd University, Budapest Budapest Business School, Budapest István Gábor Hatvani Department of Physical and Applied Geology Eötvös Loránd University, Budapest