1. Traps for litterfall and for lateral transport of organic matter were sampled over a 1‐year period along longitudinal and lateral transects in a glacial stream system (Val Roseg, Swiss Alps), which is characterized by single‐thread reaches and a large subalpine floodplain.2. Allochthonous inputs to the glacier stream were low close to the glacier terminus but increased as woody riparian vegetation and forests develop. Annual inputs varied from 0.4 g ash free dry matter (AFDM) m–2 year–1 (direct input) and 0.7 g AFDM m–2 year–1 (lateral input) in the proglacial area to 23.0 g AFDM m–2 year–1 (direct input) and 10.7 g AFDM m–2 year–1 (lateral input) in the lowest reach with adjacent subalpine forests.3. Direct inputs of organic matter decreased exponentially from forests at the floodplain edge to the floodplain centre, while lateral inputs of organic matter correlated linearly with distance to trees. Direct litterfall dominated litter input close to the forest, while lateral transport was the major pathway for channels more than 20 m away from the forest.4. A conceptual framework is developed illustrating the influence of terrestrial vegetation and fluvial morphology on organic matter input along the continuum of glacial streams.