The boat trip to Cabo in Tayrona National Park is apparently rough and the guidebook says to make sure to protect your baggage during the boat trip as it will get thoroughly splashed. Normally, I would simply place it in a large plastic bag except that Tayrona National Park has rules which include:
Entry of plastic bags and polystyrene objects is restricted.
What non-plastic cover can I use to protect an 80L backpack from splashing? It need not be protected from submersion, just regular splashing from saltwater for at least an hour journey.