Factual error: While featuring a brand-new 1962 Cadillac, a 1963 Chevrolet and 1963 Ford are shown.
Factual error: Amazon rivers have no high salinity as shown as necessary to maintain the creature.
Audio problem: When Michael Shannon fires his gun, you can hear bullet casings falling to the floor, as is normal with a semi-automatic pistol. However, his gun is a revolver, so the casings won't eject until the gun is opened and emptied manually before reloading. (01:07:10)
Answer: There are a lot of Hellboy fans who speculate this is an origin story of Abe, or at the very least the Asset is the same species, but del Torro has denied it. Abe is a copyrighted character that del Torro's Hellboy was based on, and he doesn't own the copyright. In addition, prior to The Shape of Water, del Torro was in talks with Universal about remaking "The Creature from the Black Lagoon", only making the movie center on the creature's (Gill-Man) perspective and getting together with Kay (the female lead). Del Torro has stated that the Amphibious Man is based on Gill-Man and this film is what he had pitched to Universal, but was turned down by them. Although, a creature developing a love interest in a human female isn't unique, nor is capturing a creature to study (both happen to Gill-Man, Abe, and Amphibious Man). But the fact that Doug Jones plays both Abe and the Amphibious Man only seems to strengthen theories of some connection to Hellboy, but at this point we only have del Torro's word that it's not and why he choose the creature to be so similar at this point would only be a guess.
Bishop73