Cell Block Sea (also known as Phish Farm and Serpent Turf) is a recurring challenge on Survivor.
Castaways must race out into the water and swim over to their respective tribe's bamboo cage. Once the entire tribe has arrived, each person must climb up and over the cage wall and jump into the water. They must then retrieve a large item and bring it back to shore, where a final task would occur. The first tribe(s) to finish this final task would win.
The challenge debuted in as a Reward/Immunity Challenge in Caramoan, where each tribe had to retrieve a heavy chest from the cage, then move the chest along a track and onto a platform using grappling hooks, with the first tribe to get their chest on their finish platform winning. The tribes traded the lead throughout the challenge, with Bikal narrowly hooking their final piece of track ahead of Gota to win, sending Gota to their second straight Tribal Council.
In Cagayan, the challenge was once again used for reward and immunity, with the tribes collecting four fish traps from the cage, before using the puzzle pieces in the fish traps to solve a puzzle back on the beach. Luzon took a large lead over Aparri and Solana heading into the puzzle stage, but J'Tia Taylor cost them a taste of victory when she failed to complete the puzzle. Sarah Lacina managed to finish first for Aparri, and LJ McKanas finished second for Solana, sending Luzon back to Tribal Council.
The challenge reappeared in Game Changers, again for reward and immunity, where six members of each tribe had to drag a 400-pound snake out of the cell and onto shore. The three remaining castaways had to retrieve numbered tiles from the snake, after which a code could be solved, unlocking rings which they must toss onto eight targets to spell "IMMUNITY". Nuku had an early lead with their strategy of involving every single castaway, while Mana fell behind when they had difficulty transporting their snake. However, Mana was able to catch up on the ring toss thanks to Malcolm Freberg, but Nuku managed to pull out and win again, sending Mana back to Tribal Council.
The challenge was used as the fourth Immunity Challenge in Ghost Island, in a similar design to Caramoan, but with only one piece of track to hook, and an additional stage of getting all five balls in the chest on top of a narrow perch. Malolo had a huge lead heading into the final task after Naviti struggled throughout the challenge. However, Naviti managed to catch up when Malolo could not get their final ball on their perch, allowing Naviti to come from behind and win, sending Malolo to Tribal Council.
In Edge of Extinction, the challenge was again used for reward and immunity, and worked similarly to Game Changers, except that all eight members of each tribe would now start on a floating platform instead of racing out from the beach. Kama took an early lead after Keith Sowell struggled in the water for Manu. Although Keith attempted to make up for the deficit during the ring toss portion, he only set Manu further back, allowing Kama to pull out their second consecutive victory, sending Manu back to Tribal Council.
"There's Gonna Be Hell to Pay"
"Hot Girl with a Grudge"
| Game Changers|
"The Stakes Have Been Raised"
| Ghost Island|
"Trust Your Gut"
| Edge of Extinction|
"One of Us Is Going to Win the War"
- The eventual runner-up has always been on the winning tribe.
- Andrea Boehlke, Aubry Bracco, Malcolm Freberg, Sarah Lacina, and Tony Vlachos have competed in this challenge twice.
- Andrea and Sarah won both times, while Aubry, Malcolm, and Tony have only won once.