No historical record of them in the SGZ, ZZTJ or the gazette Huayang Guo Zhi, they are an invention of the novel romance of the three kingdoms.

Spoilers from the novel chapter 89 but there is no explanation given other then "they exist, here are their powers" while they hurt becuase Shu forces are struggling in extreme tropical heat.

!In the novel in chapter 86 the Nanman forces of Meng Huo have been defeated several times so takes the (fictional) brother Meng You's advice and goes to (fictional) King Duo Si to reside in a defendable place where the poison springs are. The Nanman refuse to engage in battle and the Shu forces are suffering from the extreme southern heat. Duo Si describes the springs as "Then again there are four streams actually poisonous. One is called 'The Dumb Spring.' Its water is pleasant to the palate, but it makes people dumb and they die in a few days. A second fountain is called 'The Spring of Destruction' and is hot. But if a person bathes therein, his flesh rots till his bones protrude and he dies. The third is 'The Black Spring.' Its waters are greenish. If it be sprinkled on a person's body, his limbs turn black and presently he dies. The fourth is 'The Spring of Weak Water,' ice cold. If a person drink of this water his breath is chilled, he becomes weak as a thread and soon dies. Neither birds nor insects are found in this region, and no one but the Han General Ma Yuan, who was styled General Who Quells the Waves for this exploit, has ever passed. Now the northeast road shall be blocked, and you may hide here perfectly safe from those troops of Shu, for, finding that way blocked, they will try the other road, which is waterless save for the four deadly springs. No matter how many they be, they will perish, and we need no weapons." !<

!Shu vanguard under Wang Ping falls ill and unable to speak, Zhuge Liang prays at a temple to Ma Yuan and then treats an old man well, said fictional old man is a spirit from the mountain who rewards Zhuge Liang by guiding him to a man who can help. Turns out the new (fictional) old man is Meng Jie, elder brother of Meng Huo who views his younger brother as wrong and uncultured, is such a fan of Zhuge Liang that he provides cures and ways for Shu troops to drink safe water. Zhuge Liang has to pray to fill wells his troops have dug, Heaven grants it and Nanman become discouraged.!<

The novel fleshes out the camapign from a quick put down, once Chengdu focused on it, of a local revolt of respected local gentleman Yong Kai (then Meng Huo after Yong Kai was assassinated) with some tribal support from an inexperienced Zhuge Liang to a multi chapter epic about a master Chinese strategist against barbarians led by King Meng Huo (who is changed to a Nanman figure).

Zhuge Liang travels to a foreign land with exotic animals, unheard of armor, nasty weather and terrain against the barbarian then through his inspiring virtue and his unparalleled strategic brilliance, brings the submission of the Nanman tribe, a deed worthy of the famed Han commander Ma Yuan. A lot gets invented and it provides something different from the rest of the novel, it adds to brilliance of Zhuge Liang before his major camapigns against Wei.

In short, they were an invention of an author to liven up a minor camapign into a grand epic and adds to Zhuge Liang's glory as he encounters such strange obsticals, it adds to the exoticism of the land he is fighting in. There is no historical basis for the poison marshes of that camapign