|“||Blood waters, huh? Guess Dr. Z had a little kidney problem.||”|
|— Tom Servo|
The film begins with Nazi mad scientist Dr. Kurt Leopold in his lab, where he has lived alone for about 20 years (it is revealed later in the film that he graduated cum laude from MIT in 1934). He is contemplating his former colleagues' derision for his "formula", which is described as "ZaAt" (read Z-sub-A, A-sub-T, but which he simply calls "Zaat"). This compound, it is later explained, can transform humans into sea creature hybrids and "mutate all sea life". He injects himself with the serum and immerses himself in a tank connected to an array of equipment of an unspecified nature, emerging as a furred, fish-like monster.
His first act of revenge on the society that he feels has wronged him is to release several smaller walking catfish around the town's lakes and river (filmed in the St. Johns River near Green Cove Springs, Florida), an annoyance to the townspeople, and releases Zaat into the local water supply, rendering many of the townspeople ill.
Leopold decides to kill the colleagues that scoffed at his work. He begins with a character named Maxson. In a lake where Maxson is fishing, Leopold swims under Maxson's boat, overturns it, and proceeds to kill Maxson and Maxson's son. Maxson's wife escapes, although she is in shock from the attack.
After killing Maxson, Leopold discovers a girl who is camping out alone on the shore of the lake. He approaches her, only to be deterred by her barking dog. The girl carries on with her business, unconcerned about the barking dog. Leopold retreats. Later, Leopold kills another colleague, Ewing.
His two colleagues now deceased, Leopold returns to the lake where the girl is still camping and waits for an opportunity to abduct her. His perseverance pays off when she strips down to a yellow bikini to go swimming. She dives into the lake, swimming carefree until Leopold catches her underwater. He swims with her to his lab, even as she struggles in vain to escape.
At the lab, the bikini-clad girl is lying strapped down in a mesh basket next to the large tank of Zaat. She is unconscious, and Leopold reveals his intentions to make her his mate. Leopold injects Zaat into her neck. As she is immersed into a tank of Zaat, the girl wakes up and struggles against the ropes holding her. The equipment malfunctions for reasons unknown, and her corpse, partially transformed, is pulled from the tank.
The movie strangely diverts from the storyline for approximately 10–15 minutes to show a lingering scene of the town sheriff Lou, watching a small group of youths playing religious folk music. After one of the youths (an acoustic guitarist, Jamie DeFrates, who also wrote the songs for the film) finishes leading the group in a song, the town's sheriff, Lou, places them all in the town's jail, presumably for their own protection. (This scene does not appear in all released versions.)
Leopold attempts to kidnap another mate. His choice is Martha Walsh, the lovely female member of the INPIT scientific team sent to investigate the weird happenings in the town (caused by Dr. Leopold). Leopold grabs her after her male counterparts leave her alone. Leopold takes her to his lab, but two of her companions (having unraveled the plot) are waiting there. Leopold kills them (including the sheriff) violently. He injects her with Zaat, readies her to be dunked into the tank, and makes his getaway, with canisters of Zaat. Martha's transformation does not go as planned and she gets saved from getting dunked in the tank by one of her dying male companions as Leopold flees toward the ocean. Despite being saved from the transformation, she appears to be in a trance and immediately follows Leopold into the sea. The movie ends ambiguously, with Leopold seen shot but not killed.
- Walking catfish do exist. They are native to Southeast Asia, and are an invasive species in the United States, primarily in Florida. For more information, please consult ichthyologist Helen Dobson.
- This film was released as part of the Thriller Video VHS series (with host segments by Elvira) under the alternate title Attack of the Swamp Creatures.
- Director Don Barton filled the monster role through a newspaper ad. The ad read: "Wanted: 6'5'' or taller male to play the role of monster in horror movie. Must be experienced swimmer, scuba diver. Acting Ability not required!" Barton said ten people responded.
- Originally, the film was supposed to include scenes of gigantic catfish destroying the countryside. Footage of the walking catfish on miniature landscapes was too hokey. One shot made it into the film; a catfish squirms next to a miniature fence during one sequence.
- In an interview, writer Ron Kivett said the script was inspired by an article he read about a species of 'walking' catfish that could live in water and on land. The article theorized that the fish were possibly a mutation. Doctor Leopold refers to the same species of fish in his voice-over narrative.
- This was the only movie for most of the cast and crew. Two exceptions were Paul Galloway, who appeared in J.D.'s Revenge (1976), and one of the extras, who appeared in Silent Night, Deadly Night 3: Better Watch Out! (1989).
- The Marineland park location that was used for Dr. Leopold's lab was previously used for another monster film: Revenge of the Creature.
- Movie continuity mistake: As Leopold attempts to convert the girl into his mate, we first see her hands tied down as he gives her the injection (preventing her from stopping him, of course) but her hands are free seconds later when he dunks her (apparently so the actress could hold her nose).
- Like many movies shown on MST3K, the film was edited down to fit inside the running time of the show. In the case of Blood Waters, the original film was nearly 100 minutes long, so the MSTied version is cut by around 25 minutes, some of which includes a scene in which the chicken-legged sherrif breaks up a gathering of hippie squatters in an abandoned building listening to a song by the same folk artist who sings the film's opening theme (folk singer Jamie DeFrates, who is still quite active in the music community). The complete, unedited version of the film (from a much better quality print) can be seen here.
- Opening Scene: Crow takes up chewing tobacco. He keeps spitting the juice into soda cans, so Mike doesn't know which one to drink.
- Segment One: Crow marks the cans he spits into so Mike won't drink it accidentaly, but Tom does. Pearl deprives the SOL of love, as part of an experiment.
- Segment Two: Crow does an evil voiceover while watching Mike at the bridge, but he gets wedged in a bulkhead and Mike has to loosen him, resulting in Crow narrating falling to the floor and being smashed into several dozen pieces.
- Segment Three: Inspired by the fishing scenes in the movie, Mike and 'bots orbit over Bass Lake, trying to catch some sunnies. Nice day for it, after all. Mike catches one and reels him waaaaaay up from Earth. Unfortunately, the fish freezes in the upper atmosphere and goes through explosive decompression.
- Segment Four: Disappointed by the movie's teasing shots of women starting to take off clothes and then not doing it, Servo and Crow try to convince a skeptical Mike that any movie scene is better off with nudity. To demonstrate, they enlist Brain Guy and Bobo into performing a scene from Glengarry Glen Ross, starkers. Needless to say, it does not make their case.
- Segment Five: Taking a cue from Dr. Z's neat, portable ZaAt cases, Servo and Crow show Mike a variety of handy plastic food carrying cases, in just the right sizes and shapes. They explain it to him long, long after he's gotten the point. Down in Castle Forrester, Pearl has invented a Mer-Monkey, using a giant grouper, a Sawzall, and a Bobo. Seeing that Bobo now attracts lonely, rugged sailor men, she decides she will be become half-grouper herself, enter mermaiden-hood, and get some old salt action.
- Stinger: Dr: Z. says, "Sargassum: the weed of deceit!" over a shot of the plant.
- “rice a pipple” (Bride of the Monster)
- “Think I’ll head over to Party Beach and see how The Horror is doing.” (Horror of Party Beach)
- “I had such a pretty miiiiind!” (Girl in Gold Boots)
- "...Unless you're Doug Flutie."
At 5'10", NFL quarterback Doug Flutie was one of the shorter QBs in the league.
- "So, all roads lead to Wally Cox."
Wally Cox was a comedic actor during the early years of television, known best for playing 'Mr. Peepers.'
- "Now I'm going to fall in love with Winona Ryder, trash a hotel, maybe take a gun on a plane."
These are various activities undertaken by actor Robert Downey Jr. during his heavy drug use phase.
- "It's Andy Warhol's 'Swimming'!"
A reference to pop artist Andy Warhol's literally-named experimental films, such as Sleep and Eat, the first consisting of five and-a-half hours' worth of footage of a sleeping man, the second being fourty-five minutes of film of a man eating what appears to be a mushroom.
- "He's gonna try to win Ben Stein's money."
Win Ben Stein's Money was a 1997-2003 game show on Comedy Central where contestants competed for $5000 of character actor Ben Stein's money.
- "I gotta finish this up, then I gotta go kill Farley Granger's wife..."
- "Can't you see what I'm trying to tell you? I love you!"
A line from the 1933 film Duck Soup, starring the Marx Brothers, and a favorite MST3K riff during fight/struggle scenes and awkward verbal exchanges.
- "Open up! It's the Fish Police!"
Fish Police was a comic book series by cartoonist Steven Moncuse, adapted as a short-lived animated TV show in 1992 (Although the joke seems to be more in line with police who'd investigate matters related to fish, than fish who are police officers).
- "This is first class service..." "...And yet I still feel compelled to take a dump on the drink cart."
A reference to the case of Gerard Finneran, who became enraged when flight attendants refused to serve him more alcohol and ended up defecating on a food service cart.
- "I'll go pick up the other Banana Splits!"
Sid and Marty Krofft created the Banana Splits Adventure Hour for Hanna-Barbera in 1967. The main characters—Bingo, Drooper, Fleegle, and Snork—drove around in amphibious six-wheelers like... Um, whatshisname, the white guy... does for a while at the end of this movie.
- "I ain't got time to bleed."
This line was spoken by (former pro wrestler and future Governor of Minnesota) Jesse Ventura's character in the movie "Predator", where he famously says "I ain't got time to bleed" when told that he's bleeding by one of his compatriots. He then proceeds to mow down several guerillas with his hand-held gatling gun. Ventura later used the line as the title of a book.
- [Close-up of some unidentifiable part of a fish.]
- Mike: Please enjoy a fish anus.
- [Mad narrator Dr. Leopold discusses how the walking catfish moves.]
- Narrator: Forward progress is made with a snake-like slither and a vigorous thrashing of the tail.
- Crow [as Narrator]: ...like Courtney Love.
- [Dr. Leopold is performing a series of complex tasks with his equipment]
- Servo: I need to simplify my masturbation ritual.
- [Leopold the fish monster attacks a swimming beauty in a bikini.]
- Mike: He's a Cop-a-feel-acanth.
- [INPIT agent Martha Walsh begins to strip out of her jumpsuit.]
- Servo: Mike, how come you don't look like this in your jumpsuit?
- Crow: A-are you sure you're buying the right kind of jumpsuit?
- Mike: Hmmm...
- [Dr. Leopold lumbers into town after having turned himself into a half-man, half-catfish monster.]
- Servo: [excited] Oh! Oh! Oh! You know who they need to take care of him? Huh? Do you know? Huh? Do you know? Catfish Hunter, that's who! Ha ha ha!
- Mike: [unimpressed] Hmm... that doesn't really work for me. See, the guy changed his name.
- Crow: Yeah, to Catfish Chapstick, so the joke doesn't work.
- Servo: [deflated] Oh... but it was a good joke! Wordplay like that doesn't come around so often.
- Mike: But it only works if you get the correct, current name.
- Servo: [disappointed] So the joke doesn't work? Sheesh...
- . . .
- Mike: Tom, are... are you sulking?
- Servo: [angrily] No!
- Mike: Yes you are, look—look, I'm sorry. It was a good joke...
- Crow: No! No it wasn't, Mike, 'cause his name is Catfish Chapstick...
- Mike: Ssshh! He's suffered enough.