Closely cropped algal turfs are characteristic of healthy coral reefs, but unchecked growth can cause transitions into long sediment-laden turfs, which may be an alternative degraded state. While control by herbivores is well established, potential interactions between nutrients and macroalgae have not been evaluated. We varied macroalgal presence and nutrient addition and measured turf height and sediment accumulation over 18 d on an algal-dominated fringing reef. We found a novel facilitative effect of macroalgal presence on turf height as macroalgal presence increased growth by 34% over its absence. Nutrient addition also significantly, but independently, increased turf height by 127% compared to no nutrient addition. Macroalgal presence reduced sediment accumulation, possibly by trapping the sediment and/or by a whiplash effect. Thus, overfished coral reefs experiencing macroalgal blooms and/or nutrient additions may be at risk of developing long algal turfs, which could maintain a persistent shift to a degraded state.