Krinix says,

”It looks like we have 2 objectives here: find what’s at the end of this tunnel, and also find the source of this water’s corruption. It appears to have some taint.”

Krinix would like to get a stick or dagger or something from one of the corpses and dip it into the water, to see the reaction, and to try to determine if there’s oil on top of the water.

Qiran keeps his distance from the suspicious water.

"Corpses tend to foul the water, and grubs tend to become another thing.  What do corpse larvae become?"

Something unexpected happens when the dagger with the infected orc's blood touches the water. The rotting scent of the grubs becomes intensified as soon as the water comes in contact with it, and a sickly red crust forms on the tip. The blood seems to bubble and then harden into a kind of cocoon-like substance, similar to the kind of goo the larvae shoot.

Kronos sighs and drops the dagger (not in the water). 

“This does not appear to be a simple matter. Shall we explore further?”

Chroma nods, intrigued at the curious nature of the water. "Let's press on. This place has indicated to be of great value to Phlan, and the purpose of the venture is to solve the issue with the water."

“Yes, let’s go down that branch where the grub-things seemed to want to go. I’d worry about what’s down there and wouldn’t want it at my back.”

“But let us proceed cautiously and quietly, I’m not sure of the stability of this area.”

Qiran quietly falls in along with the others.

"At least their flesh-husks do not retain much strength.  And if this is an infestation, we should cleanse before another flesh-source is found."

"These... don't seem natural..." Faerieth comments.

The journey down the tunnel is disturbingly quiet. There's no noise aside from the trickle of foul-smelling water. The rotting stench gets worse as they continue, until a red haze tints the light. At a juncture that climbs upwards, the group can see some kind of obstruction, but the smell is so powerful it's causing the group's eyes to water.

Everyone make a constitution save roll: DC 8 to resist the choking fumes. It's enough to make you want to vomit.

Constitution Save: 4

Chroma’s save: 13

Faerieth starts to feel nauseous at the intense smell of death coming from whatever is blocking the tunnel. Littering the tunnel floor, too, are old bones and lumps of meat too putrid for the creatures to stomach. The haze is hard to see through... but those who aren't dry-heaving can see dozens of shambling shapes... not just orcs, but ogres, bugbears, and goblins. It seems that the survivors of the liberation of Phlan fled to these tunnels when Tyranthraxus fell. They've been stumbling about, infested by these parasites for years in this living death.
Worse yet, the infested are carrying armfuls of sticky, pulsating gore and are moving further up the tunnel, like ants following a scent trail.

14

Qiran recoils, with a save of 21

The group is far enough away from the horde that they either can't see them or don't care that they're there. The population here seems to all be focused on delivering whatever disgusting red sludge they carry to whatever is behind the red haze.
A steady pulsing sound can be heard echoing from further down the tunnel. It almost sounds like a heart beat.

((Should we do like the walking dead, cover ourselves in red sludge and join the horde?))

Krinix says,

“Oh dear, that’s rather more enemies than I’d care to handle today. Or perhaps ever. Shall we go the other direction?”

Quote from T0dd0 >>

((Should we do like the walking dead, cover ourselves in red sludge and join the horde?))

(DEFINITELY NOT)

Faerieth has to double over to vomit for a while. The stench, the sight, everything. When she finally gets back up, all she whispers is, "This... this is not natural..."