Brown Trout (Salmo trutta) are a game fish that have been introduced all over the world, including New Zealand, to the joy of many freshwater anglers. However, they are not loved by all camps with many arguing that they cause trophic cascades that reduce ecosystem health and make rivers very green. This study investigates the relationship between brown trout and the food web within a popular river in New Zealand’s capital city. We make use of a long term monitoring dataset to assess trophic patterns over time and assess whether changes are driven environmental or biological factors. We then assemble and use a quantitative food web model to simulate the effects of trout density on food web structure.