Water Resour Manage (2009) 23:1125–1135 DOI 10.1007/s11269-008-9318-9 Using NDVI from MODIS to Monitor Duckweed Bloom in Lake Maracaibo, Venezuela Lawrence M. Kiage · Nan D. Walker Received: 24 March 2007 / Accepted: 7 July 2008 / Published online: 1 August 2008 © Springer Science + Business Media B.V. 2008 Abstract Four summer time-series (2003–2006) of Normalized Difference Vegeta- tion Index (NDVI) derived from MODIS imagery were used to investigate duckweed blooms and other floating vegetation in Lake Maracaibo, Venezuela. Preliminary findings revealed the presence of duckweed and floating vegetation in the Lake during summer in varying amounts (0–11%) that appeared to be related to satellite- derived rainfall anomalies from the Special Sensor Microwave/Imager (SMM/I) during the previous month. The first appearance of duckweed in abundance in 2004 and its reappearance at similar levels in 2006 may indicate a response to increasing nutrient loading in the lake. The duckweed rafts may be an environmental warning of imminent ecological disaster that needs to be mitigated. MODIS data, with its daily repeat cycle and 250 m pixels showed great potential for monitoring floating vegetation in the lake. Keywords Lake Maracaibo · Venezuela · Eutrophication · Duckweed · MODIS · NDVI 1 Introduction Eutrophication of water bodies such as lakes and estuaries is one of the most serious water quality problems worldwide. Although eutrophication is a natural process in the aging of lakes and some estuaries, human activities (e.g. agricultural runoff, urban runoff, leaking septic systems, sewage discharges etc.) can greatly exacerbate the L. M. Kiage (B ) Department of Geosciences, Georgia State University, P.O. Box 4105, Atlanta, GA 30302-4105, USA e-mail: lkiage@gsu.edu N. D. Walker Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA