Badass Grandpa: Jeremy Wade is somewhere in his fifties, and he hunts out fish that can reach twice his weight.
In dangerous conditions like; at the base of a waterfall, during lulls in border conflicts, surrounded by bears, crocodiles and hippopotamuses, whatever else is hiding in the tropical rainforests near both the Amazon and Congo Rivers, or on the icy waters of an Alaskan lake. He's also suffered numerous injuries and even survived a plane crash and is still going!
A few of the fishermen he goes to for advice on catching the fish that he is going after are at least past their fifties and have been catching these fish—sometimes without bait or tackle—in some of the most dangerous rivers and lakes in the world for decades.
Badass Teacher: One of Jeremy's previous occupations prior to River Monsters was as a biology teacher.
Bears Are Bad News: An episode in Alaska showed Jeremy having an unnerving run-in with a grizzly, as mentioned in Revolvers Are Just Better below.
Bloody Murder: The longfin eels Jeremy investigated in one episode have poisonous blood.
The Catfish: Including several literal species of catfish.
One episode focused on the various kinds of catfish Jeremy has encountered during his travels.
Cluster F-Bomb: Jeremy lets loose with one of these when trying native fishing techniques in one episode, actually having been encouraged to cuss out and insult the fish while trying to catch it by one of the locals teaching him. The result borders on Crowning Moment of Funny.
Another time he got stabbed in the back of the hand by the pectoral spine of a catfish, eliciting quite a few bleeps from Jeremy in response.
Death from Above: In one episode, Jeremy and his film crew were nearly hit by lightning when caught out during a sudden thunderstorm. One of the crew actually had a headache and was nearly knocked unconscious, suggesting he might have taken a peripheral hit from the strike.
Determinator: Jeremy's response to a Colombian stingray breaking his rod (but not his line) was to grab the line and haul the creature up towards the boat with his bare hands.
Doing It For Science: He very rarely kills the fish (or eats them), usually letting them go and even giving them a few minutes' rest if they need it. This serves as an extreme Technical Pacifist stance, since the titular river monsters are known to kill or maim people (some of them intentionally hunting people out), and all of them come close to killing him.
In the Nile Perch episode, he risked crocodile attack while holding a captured perch by the boat so that it could recover before being released.
During his fishing trip into Chernobyl, Jeremy was shown to be quite conflicted about catching a radioactively contaminated fish for science to dissect.
Everything's Even Worse with Sharks: Bull Sharks, as he investigates, are not only capable of hunting in fresh water, but seem to be actively moving inland for the chance to dominate new territories and feeding grounds.
Food Chain of Evil: Everyone knows Piranha eat people, but Arapaima eat piranha! So do dolphins incidently. Also the episodes titular Demon Fish will have a go at Crocodiles if given the chance. Which also pose a hazard in fishing, but not as more as hippos; which have goring tusks, a habit of charging like a boar on land, surprising speed and agility in the water, and the jaw strength to snap a Croc in half! There is a very good reason the crocodiles leave the hippos a wide berth, even if they are herbovores. He even managed to catch a giant stingray, that may have been a close relative of the one that got Steve Irwin, but he still won't pick a food fight with wild Bears.
Ghost City: One episode had Jeremy visit the Ukrainian city of Pripyat, a city that was abandoned following the Chernobyl nuclear accident and has been deserted and left to rot for over 30 years.
Going Native: Jeremy goes to great lengths to ingratiate himself with local populations and often employs native fishing techniques alongside his own modern methods. He also frequently reminds viewers that, no matter what country you go to, the locals are far more knowledgeable about their home environments than you are and maintaining good relations with them can provide a treasure trove of information on many different subjects.
It's even pointed out that native fishermen wouldn't use a particular technique for multiple generations if it didn't work, as is showcased in several episodes. Jeremy agrees.
Gonna Need More X: Played straight in the giant freshwater stingray episode when Jeremy hooks into one so big that it starts towing the boat he's in. The stingray later ends up snapping a heavy-duty saltwater fishing rod designed to handle Marlin!
Gorn: Several episodes have shown images of people with horrific injuries inflicted by the fish Jeremy's searching for. Taken Up to Eleven in a couple of the South American episodes showing autopsy photos of human bodies half-eaten by piranhas and candiru-acu.
It does go a bit overboard sometimes, to humorous effect. A good example is the episode about the sea lamprey, which has rapid-fire-edit clips of people screaming and thrashing and being dragged through the water like Jaws himself was attacking them when the fish in question is a skinny four-foot eel-like critter that suctions onto prey and pokes a small hole in it to drink blood.
Groin Attack: In the first episode of the third season, the Pacu he was after has been known to do this in New Guinea, where it is an invasive species.
Also the candiru; a parasitic catfish that normally targets the gills of other fish, but has been known to embed itself in the genitals of luckless humans relieving themselves in South American waterways.
One caller to a radio talk show in New Zealand recalled an incident where a longfin eel bit a guy in the groin.
He Who Must Not Be Seen: Several episodes have had peoples' faces blurred out, most notably Ukrainian military personnel manning checkpoints in the Chernobyl episode.
Hiroshima as a Unit of Measure: A biologist Jeremy talks to in Ukraine doing research on the long-term effects of the Chernobyl disaster says that the amount of radiation released when the plant exploded was several hundred times that released by the nuclear bomb dropped on Hiroshima.
Idiot Ball: In the wolf fish episode, Jeremy points out a storm cloud some distance away that apparently had passed them by. Immediately after noting that tropical weather can be unpredictable, Jeremy, his crew, and his guide stop so the guide can get some fish for eating. They stop on a flat island, in the middle of a river, with all sorts of equipment. The sound guy gets struck by lightning.
Implacable Fish: The Giant Snakehead: a creature capable of surviving getting shot with a harpoon to the mouth from point blank range, then driving the back end through the attacker's head, killing him.
Infant Immortality: Averted. Several episodes involve the deaths of young children, who are much more vulnerable to attack because of their small size, inability to swim, or naivete to the dangers that might lurk in local rivers.
Land Down Under: Jeremy has been to Australia on three occasions (once for bull sharks, once for a saw fish and once for a relatively rare type of shark that was only recently identified.). Not as often as you'd think though given Australia's reputation, but we just don't have much in the way of the big river systems to generate the diversity found elsewhere.
Nature Documentary: Sadly, it's one of the few animal-focused shows that Animal Planet still airs on a regular basis. Ironically, this might explain its high popularity as well.
In one episode, a caller to a radio talk show in New Zealand recalled witnessing a longfin eel entering through the backside of a sheep and devouring its internal organs until the sheep died.
Perma Stubble: Jeremy can often be seen with varying degrees of this, particularly when he's spent days out in remote places where personal grooming isn't exactly practical.
Pet the Dog: The episode about the Goliath Tigerfish. After failing to catch a tigerfish three times, he requested a good-luck fetish (not that kind), slept with it under his pillow, and caught a tigerfish the next day. Jeremy planned to let it go, but was told by his native companion that the fish was a gift from God, and the neighboring village was going through hard times to boot. After several minutes of wrestling with different facets of his morality, he decided to let the tigerfish go only if it was well enough to recover. It wasn't, which disappointed him, but the ecstatic reception he got when he hauled it back to the village probably more than made up for it.
They've also popped up almost constantly in episodes shot in South America, and Jeremy frequently references them in other episodes as well. In several South American episodes he's noted that his real piranha problem is that they're always stealing his bait.
Pop-Up Trivia: River Monsters: Unhooked; reruns of past episodes with this trope added to them.
Revolvers Are Just Better: When fishing in Alaska, the guide accompanying Jeremy carries a massive revolver for defense against bears; they later end up having to fire a warning shot when a bear approaches the group after having stolen a salmon Jeremy had hooked.
The Scapegoat: A rather grim example: In one episode, Jeremy visits the Congo to catch a reputed killer fish. Not long after he arrives, the village chief's brother goes missing. Since the locals believed that there's a cause for everything, they soon concluded that Jeremy had something to do with his disappearance. Luckily for Jeremy, the chief's brother makes a belated return later into the night, for if he hadn't come back, the villagers were going to stone Jeremy to death.
Often, Jeremy discovers a fish's bad reputation is often a case of it being blamed for attacks committed by other river creatures such as crocodiles or sharks or simple unfortunate accidents.
Scenery Porn: Many locales Jeremy has visited have breathtaking sights, but possibly none moreso than Kaieteur Falls, a massive 741-foot waterfall in Guyana he visited at the finale of the last 4th-season episode, complete with dramatic aerial footage.
Screw This, I'm Outta Here: After catching a massive Wels catfish in a river in Spain, Jeremy had planned to hold it in the water until it had fully recovered, but when it started to move he ended up racing for the shore anyway.
Shout-Out: One episode had a scene showing piranhas attacking swimmers at a South American beach, the scene being a direct imitation of the beach attack scene in Jaws.
Title Drop: Jeremy often does this during the opening narration for each episode, followed by a graphic showing the name of that episode in case you didn't catch it the first time.
World of Badass: Aside from the monster fish, Jeremy sometimes encounters fellow badass fishermen and naturalists.
In the Nile Perch episode, two of the veteran fishermen are crocodile attack survivors and one survived a hippo attack. One of the crocodile victims had his leg amputated and was still fishing.
In "Killer Torpedo" he met a man who had been shot, bitten by an eel, lost a leg to gangrene, and various other injuries.