Travel 50 meters on a zipline without unhooking. The easiest way to achieve this is to just build 50 platforms out from your raft and secure ziplines from one end to the highest elevation on your raft. If you do not have a higher elevation just build a platform for this purpose and break it later. I suggest building with triangles, it may take more resources but Bruce (shark) won't break it as easily before you can complete the achievement.