A weird little fellow, the longest of the theropods was relatively lightweight compared to its contemporaries. In a region with predators such as Carcharodontosaurus, Spinosaurus was definitely not the top dog. It ate on fish, hunted small animals but mostly kept away from Carcharodontosaurus to avoid confrontation, but its sail and large tail could serve to threat display the contemporary sauropods. In a fight, however, Carcharodontosaurus would win.
Spinosaurus reached a maximum size of around 16 metres and like 6 tons or something of so but I believe its more likely that it was a teeny bit smaller because animals rarely reach their top sizes
It could definitely swim as dinosaurs were naturally somewhat adept at swimming, but definitely not as good as say crocodiles, but they did spend quite a bit of time in water
I have rather conservative views on dinosaurs