To obtain the Coast Guardian side quest in Dead Island 2, approach the lifeguard hut on the beach.
You’ll then need to take out all the zombies surrounding it. Once you’ve accomplished that task, check on “Mr. Dependable” in the hut. Next, make your way to the police station near the beach to find out the survivors are not there. Next, travel northeast towards the shops. Clear out the zombies wanting in then press the switch to the left of the garage door. A surprise awaits you inside!
Once you take care of it, return to Burt. The lifeguard hut will again be under attack. Wipe them all out then speak with Burt to have him confess what really happened. Afterwards, the Coast Guardian quest will complete. As a reward, you’ll receive 3,000 XP and 300 cash.