Seasonal variability, understood as intra-annual patterns in the rise and fall of river levels, has implications for ecosystems and the populations that inhabit them. Despite the growing hydropower generation in tropical countries, there is little research on how dams alter these patterns. Most conclusions have been drawn from rivers in other latitudes with different seasonal characteristics (Chong et al., 2021). Recognising that seasonal variability downstream of dams not only responds to seasonal climatic patterns and long-standing socio-natural interactions (Jackson et al., 2022) but also reflects fluctuations in energy market (Krause, 2017), the aim of this paper is to describe the complexity of the new conditions imposed by a hydropower dam on the seasonality of stream flow in a tropical river. To advance in this, we analyzed seasonal patterns of daily, weekly and monthly flows in three Colombian rainfall dominated rivers before and after damming and explored their relationship with the energy market. A composite methodology was used for the statistical analysis of the time series, their entropies and signal frequencies. The results suggest that in tropical rivers, hydropower dams decouple stream flow from precipitation, reduce stream flow harmonics, amplitude and intensity at monthly scale, and increase peaks frequency and number at weekly and daily scales. Dams, also reduce stream flow standard deviation and transition gradualness at sub monthly scales. We show how the use of a single index masks changes in seasonal diversity and tropical river variability and illustrate how the dominant frequencies of the energy market regroup stream flow variability on different time scales.