The Codon Stream is the system of rivers of "Green lava" that spread throughout Primus. The stream originates in a volcano, which is actually the processing plant for the DNA of the stream. Originally, there was thought to be only 10,000 forms in the Omnitrix/Ultimatrix (as proof from the episode Ben 10,000). But Azmuth has revealed that there are samples from every sapient species of every world in the Milky Way Galaxy: over 1,000,000. As confirmed by Dwayne, two of these samples include Osmosian ( Kevin and Aggregor' s Race) DNA and the DNA of Pierce (one of the plumber kids Max trained)'s alien heritage, though Dwayne has not confirmed if or when Ben will access them. In the episode War Of The Worlds, it was stated there were exactly 1,000,903 samples currently in the Codon Stream. It was believed that this included Zs'Skayr, who had added his DNA by possessing the Florauna that was sampled, and that the extra three were from Zs'Skayr's minions Dr. Vicktor ( Benviktor), the Mummy(Benmummy), and the Yenaldooshi(Benwolf) who accidentally gave Ben their forms during their encounters with him. Furthermore, in the movie "Race Against Time", Ben was forcibly given the form of Eon (Ben questioned if he could use Eon again in the movie but Eon soon showed up saying he no longer had Eon's form within the Omnitrix though Dwayne McDuffie has confirmed otherwise). However, it was revealed in the episode "Ghost Town" that Zs'Skayr had been removed from the Codon Stream and imprisoned prior to Alien Force (but was readded in the same episode), meaning that by the end of the original series, there were exactly 1,000,904 alien forms. As four of these aliens were picked up by Ben, there were exactly 1,000,900 samples in the Omnitrix when Ben found it and given that one of these wasn't intentionally added by Azmuth, it is estimated that there are 1,000,899 beings in the Milky Way that were originally intended for the Codon Stream. Ben's variety of alien forms hasn't stopped increasing there. In the movie "Alien Swarm", Ben gained the form of Nanomech from the Hive (unlike Eon, Ben was able to fully control it and it appears in Ultimate Alien), which made 1,000,905 DNA samples. More recently, Ben has obtained the samples of five aliens from the Andromeda Galaxy named Bivalvan, Galapagus, P'andor, Andreas and Ra'ad, resulting a grand total of 1,000,910 samples, making another set of aliens.
Connection to the Omnitrix/UltimatrixEdit
The river has a special connection to the Omnitrix, Ultimatrix and Azmuth's third Omnitrix, with the fact that the Omnitrix/Ultimatrix is actually a wireless receiver connected to the Codon Stream, allowing the Omnitrix/Ultimatrix to alter the current DNA of its user.
When activated, the Omnitrix/Ultimatrix opens up a holographic display of all aliens unlocked. When the faceplate is pushed back into place, it emits a signal that is picked up by the volcano on Primus, then sent throughout the Codon Stream, and back to the Omnitrix/Ultimatrix, with the selected alien's DNA attached. The DNA is then sent to the users current DNA, and modified to fit the aliens DNA, and turn the user into the selected alien. This could be why there's a green background every time Ben turns into an alien in Alien Force. In Primus, it can be shown that someone can absorb the energy of the Codon Stream to become more powerful. Vilgax demonstrates this when he falls into the Codon Stream and grows 100 ft. tall. But soon the effects wore off and Vilgax returned to his normal size. If Primus or the Codon Stream are destroyed, the Omnitrix/Ultimatrix or any similar version, will become utterly useless and literally neutralized
By technicalites with the introduction of the evolutionary function there should now be at least 2 million samples in the codon stream. It is not 2,001,820 samples because as CN Action Pack shows the Appoplexian race doesn't gain an evolved form, which suggest there are some species that don't survive 10,000 years of war ridden combat.