Get prawn suit depth mk1 if you want, but most of the lost river is explorable, however you will need mk1 to explore all of the lost river and mk2 to explore the active lava zone. You dont need any specific tools other than your prawn, but get the jump boost if you want to get back out. You also need a purple tablet for the base in the lost river and 2 purple tablets for the two bases in the lava zone. You should go there as it progresses the story, I recommend you get the reinforced dive suit. I also recommend the repulsion cannon as my prawn often gets stuck in alien bases.

Alrighty, thanks bro

if you are taking the cyclops into the ilz you MUST have the suppresion system