One of the main problems with it is the canal will go through lake Nicaragua so each time they open the lock a bit of salt water will get into the lake, when your talking about a lock big enough to take a 400,000 ton container ship won't be that long before the lake starts turning brackish. Yes lots of wildlife will suffer a 500 m wide canal going through the rainforest is not a good thing, also Costa Rica is concerned about the pollution contaminating there lakes and rivers