The River Otter is a rather large predator of fish of all kinds. In a pond they are devastating because the fishing is so easy. Their fishing style is detailed below. River Otters tend to live on river banks and if your pond is near a river, your odds of a terrible encounter increase radically. IF the River Otters find your pond and fish, expect extremely heavy if not total mortality.

So. Let’s open by saying, “You Probably Can’t Actually Kill or Remove The River Otters.”

But you can control them. They are visual hunters and prefer to hunt at Dusk or Dawn. And they don’t depend on the fish being asleep. They do benefit from the fish being trapped in a pond because they get endless “try after try” to catch the fish.

The “fix” for River Otters is at the end of the article. But here is my personal experience, unadorned.

Hi group. Help needed. In almost 30 yrs of dealing with pond predators I’ve never experienced otters. Until recently. I just had a client’s pond get completely wiped out overnight. 30+ koi, most over 18″. Caught the bastards on security camera. All of the fish torn to pieces and eaten except for two that are severely injured and now back at my shop in a salted tank. Client is completely devastated, I’m worried because my house and pond full of koi is only a couple of miles away. Traps have been ordered. I think they got another client’s pond last fall. Anybody have a deterrent? I’m shooting on sight, protected species or not, but they’re nocturnal and very sneaky. Thank you in advance

When my entire collection was wiped out by River Otters in 2009-10 I was stunned. They are amazing hunters, the style is to push off the bottom and bite off the tails of the biggest fish. When the fish is helpless they drag it away to the kits. A “family” of River Otters is the end of you. They will stay near the pond and eat until it’s empty. And if you restock too soon, you are only feeding them. If you try to shoot them, it is a fool’s errand because you will puncture the liner where they stand. Additionally, they really don’t like daytime hunting. I had the US FIsh and Wildlife Service out (well, a friend of mine was a ranger hahahaha) and he came out and said I needed traps. There was scarecely anything else that would work. That if you can find where they come in, and put one of the guillotine traps in that path, you got ’em. Problem was that the pond had a dozen points of safe ingress. At the time they did not have the kind of motion detectors they have now. My “Blink” camera is battery powered and can detect a squirrel and Mocking bird. I know, I’ve seen it do it. At THAT rate you could, potentially murder the perpetrator, -OR- get the metrics needed to place your trap propitiously. I wish you luck. I never defeated the Otters. They defeated me in three re-stockings. They even think Feeder Goldfish, and Catfish & Bass fry are worth eating.

The question was posed to a group of top pond installers and maintenance experts, and the consensus was POND DYE. Different ideas such as motion detectors, specialized electric traps, getting a dog (which doesn’t usually work) and more. But 3 out of four of the recommendations were black dye. And that makes sense because River Otters are absolutely VISUAL feeders. Here’s Pieter:

Pieter van Westervelt – Top Contributor
“Unfortunately the best thing is pond dye. If they can’t see their prey they move on. And even worse is they will continue hunting a pond for years once they know it’s a food source. So I wouldn’t rush to restock your clients pond, and when you do use the black dye.”

https://amzn.to/4aVDBfh

Jeff Chudek Moderator
Top Contributor
I’ve heard electric fencers work for otter/mink as well. Not sure how we would do with snow.

Dennis Rodriguez
A member of our local koi club had the same thing happen to him three years ago. We had a very cold winter that year and apparently the otters had very little wild food available in their habitat so they got out their norma hunting grounds and wiped his pond. He installed an electric fence/wire all around his pond perimeter and also on top of his property fence and I don’t think he has had any other otter attacks in three years.

Ian Menzies
The fence you see in the back ground is electrified. The galvanised mesh at the base is buried a foot in the ground. This was installed a few years ago and seems to work well.

Marvin Siderius Top Contributor
We have a few ponds with electrical fences. Average voltage 6800 V. Use a digital tester and test at many spots.
So far so good. Make sure all areas are covered.
We typically run 3-4 wires.

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The “Cure” for Ammonia issues in a pond or aquarium is BIOSEEDING. This is the simple (it is simple) transplant of beneficial germs and microbes from a natural body of water, or an established fish system, into the immature system which lacks those organisms.

What organisms are lacking?

How do I do “Bioseeding“?

About Ammonia as a Fish Killer

Ammonia: Most Common Killer of New Fish

– By Dr. Erik Johnson
Ammonia is the primary waste product of fish, excreted primarily through the gill tissue, but to a lesser extent via the kidney. Ammonia can also accumulate from the decay of fish tissues, food and other organic debris derived from protein. Ammonia accumulations cause reddening of the skin and disability of the gills by its direct caustic effect on these surfaces. Fish suffering in water with high ammonia accumulations will isolate themselves, lie on the bottom, clamp their fins, secrete excess slime, and are much more susceptible to parasitic and bacterial infection.

Ammonia is a big problem in new systems because the bacteria that would naturally dissolve ammonia are not established, see discussion of cycle. As well, even in established systems, ammonia may accumulate in springtime when the water is cold but fish are eating, because filter bacteria have not emerged usefully from hibernation.

Ammonia ionizes below pH 7.4 to Ammonium – and so in its ionized state is less toxic to fish.
Above pH 8.0 most ammonia is ionized, and so becomes more toxic. Care should be taken not to increase th pH of a system if ammonia is present but the need to drop the pH or restrict oxygenation to tanks of fish to keep pH down is an overrated aberration in the literature.

Treatment: Water changes and management of the pH near neutral will go a long way to cutting losses from Ammonias, ancillary, less useful modes of Ammonia management include the use of the various water conditioners that bind ammonia, and the application of rechargeable Zeolites to the system filter. I am still going to tell you that time and water changes are the two mainstays, however.
Water that is warm, high in pH or deprived of oxygen will have an enhanced toxicity when ammonias are accumulating. These are all important considerations as we try to interpret the varying symptomatology of fish at the same ammonia level, for example, but are affected very differently.

You will never have to worry about Ammonia if you use a drip irrigation system for constant water replacement at about 10-20% per week.

More about ammonia

Ammonia – Understand this! – by Doc Johnson
Ammonia is the first waste product of your fish. It is often the cause of your first mortalities in new facilities and new ponds. There is a simple test to measure the levels. I am a big fan of Kent’s Ammonia Detox to reduce the toxicity of ammonia, and of Enviro Reps BRF13A (Ammo Down) for the seeding of beneficial bacteria to reduce the ammonia on the long term. Bioseeding may be the most effective method of all, when possible, and AP’s AmmoLock is great. I do not like Amquel. At all.

1. Made from rotting fish wastes/urine/food
2. Tested with Nessler’s Drop Type tests
3. After (the regrettable) addition of aldehydes such as Formalin or Ammonia-binder agents, test with Salicylate reagent tests.
4. Ammonia causes redness of fins, general poor health, excess mucus production, flashing, and by chronic auto-intoxication: Pinecone disease.
5. Ammonia is more toxic at pH above 8.0
6. Ammonia is directly irritating to fish gills and tissues
7. Ammonia is removed from the environment by beneficial bacteria called “Nitrosomonas”.
8. You can control Ammonia with partial water changes or addition of Zeolites.

I discourage the use of chemicals for Ammonia binding. All but a few of them contain aldehydes (glutaraldehyde) which are guilty of binding oxygen and irritating the fish.

Wet dry filtration (versus submerged media) is very superior for supporting nitrifying bacteria.
I will upload a VERY lengthy discussion of Ammonia in *doc format please check the downloads section.
There will also be a pretty-rare document there showing Gratzek’s research on my favorite ammonia binder, Ammolock II

Additional notes:
“First of all, because it is foiled by fewer organic molecules, let’s establish that Salicylate test kits are superior to Nessler’s tests. Still, Ammonia testing can present a problem. You may not know that dechlorinator can zero-out your ammonia test. The reason is that in the salicylate test kit, chloride ions provide a reagent. Ample dehlorinator and other ammonia binders will zero out this free chlorine reagent and show you a zero test. The only way to be sure that the Ammonia is truly bound up is by “live-tissue cell culture histopathology”. Cells are bathed in test-water and then examined for tell-tale signs of Ammonia damage. The only company that has done this so far is Aquarium Pharmaceuticals who used Drs Lukert and Gratzek at UGA. This Ammonia binder does not contain any aldehydes. Even the so-called “Sulfide Ion” binders are often nothing but Formaldehyde-bi-sulfite (rongalite) which is incredibly unstable.” Doc Johnson

Pond Clean Out Needed? How to Fix / Clean Out an Ecosystem / Gravel Pond or Water Feature?

I had “the boys” out to clean out a pond I’ve neglected for NINE years. Sure I did water changes and sometimes I’d clean the filter, but it was pretty neglected. You couldn’t see the gravel in the bottom because of the layer of leaves and mulm.

Two “Johnsons” in my family decided to be pond managers / installers and one’s my son Lock Johnson and one’s my nephew Parker Johnson.

https://www.beholderaquatics.com/
(706) 851-4425
Lock Johnson
https://www.facebook.com/profile.php?id=61554823165580

https://thepondfixer.com/
404-532-9276
Parker Johnson
https://www.facebook.com/profile.php?id=61557221360366

• Parker was trained / mentored by Mark Carter in Tennessee. Mark Carter is a Certified Aquascape Contractor with probably 30 years experience.
• Lock was trained by Pond manager / installer Rich Carter (no relation to Mark) in Marietta at Kol Koi.

So both guys have a lot of high quality experience. They’ve only ever done it right.

In managing the pond in Canton (my shame, 9-years-neglected) I got to see both managers in action. I admired that they took great care with the fish, were cognizant of shooting the liner with pressure washers, avoided illness in the fish through proper handling, and cared for the pond like their own. They know better than to sterilize the pond. And they know how to leave “just enough mulm” to avoid clouding after the cleanout.

I HIGHLY recommend either of these two resources in the Atlanta area. Their pricing is fair and their availability is good, at this time but of course they will be getting busier and busier.

Check out their Facebook pages and websites.

Thanks,

Doc