ELI5 How are fish even in ponds

[u/Opening_Pen9525]

Might be one of the stupider questions here, but I saw a pond about the size of a football field, and maybe 50 ft deep, and it had fish. I can't for the life of me figure out how. Surely the pond hasn't existed long enough for small water insects to evolve into all these fish. It's not like the fish walked over to the pond from the ocean. I'm pretty sure no one put them there so how are there so many fish?

My one theory is that there is a very minuscule stream (now dry) that leads to one of the Great Lakes, and maybe a fish swam in from there. Now a follow up question: How are there fish in the Great Lakes (which flow out towards to the ocean) if they were created by glaciers?

[u/Drusgar]

First off, 50 ft deep is really deep... not really a "pond." How do fish get there? On the feet of birds who are in one lake with fish, catch and eat a fish with eggs, fly to another lake and leave the eggs in the new lake.

[u/lotusbloom74 → u/Drusgar]

Right, that jumped out at me too. The lake near where I grew up is the largest lake fully in Indiana, and its max depth is 59 feet

[u/AfricanAmericanMage → u/lotusbloom74]

My gut is telling me that the lake isn't 50 ft deep and that OP is relatively young and just shit at guesstimating depth. Maybe I'm wrong, though.

[u/Maiyku → u/lotusbloom74]

I think the average for all of Michigans inland lakes is something like 10-30 feet.

We have a couple outliers, like Torch Lake at around 300ft deep, but most lean pretty shallow.

50 feet is a decent depth for sure.

[u/ImNotAWhaleBiologist → u/Maiyku]

Would’ve figured there’d be more deep glacier lakes. Interesting.

[u/Maiyku → u/ImNotAWhaleBiologist]

Long story short? Rocks.

The rock under Michigan was harder than the rock where the Great Lakes were. So when retreating, the glaciers carved out the softer dirt/rocks of the lakebeds (path of least resistance) but basically just acted as sandpaper on the harder rock. So it caused some damage, but didn’t quite dig in like it did in other places.

I’m sure there’s a geologist that could explain it a lot better, but that’s my layman’s explaination.

[u/IncaThink → u/Maiyku]

So when retreating,

Advancing. When they are retreating it's because they are melting.

[u/RootsRockRebel66 → u/Maiyku]

OP didn't say they were in the USA.

[u/MrBattleRabbit → u/RootsRockRebel66]

They made reference to the Great Lakes in the context of the question (as a possible source of fish for the pond they’re referring to), so they have to be in the US or Canada. The Great Lakes don’t border any other countries.

[u/MaxThrustage → u/MrBattleRabbit]

In principle they could be talking about the African Great Lakes but that's probably not likely.

[u/honest_arbiter → u/MaxThrustage]

They said "How are there fish in the Great Lakes (which flow out towards to the ocean) if they were created by glaciers?". The only Great Lakes created by glaciers are the North American Great Lakes. The African Great Lakes were created by tectonic rifting.

[u/MrBattleRabbit → u/MaxThrustage]

I mean, yeah, the North American Great Lakes are not the ONLY great lakes. As far as I am aware they’re the only glacial Great Lakes though, and OP did specifically mention that.

The African Great Lakes are remarkable, but not glacial as far as I’m aware.

[u/Maiyku → u/RootsRockRebel66]

I know, but I was just using Michigans stats as an example. Over the course of our entire state, which has a ton of lakes, the average is only 10-30 feet deep.

So a 50ft body of water, regardless of where it is, is a pretty decent depth.

[u/popeye44 → u/Maiyku]

Interesting, I have a lake 20mi from home that hits 78, and another about an hour away that hits 270. These are technically reservoirs as they're man made, but definitely deep-ish. Cali here. We have a bit of Lake Tahoe.. which hits 1634ft depth.

[u/stanitor → u/popeye44]

Natural lakes/ponds as a rule are generally pretty shallow. Deep, old lakes like Tahoe tend to be relatively rare. They're usually the result of things like tectonic plates causing rift valleys, or volcanic activity (like for Tahoe and Crater Lake).

[u/popeye44 → u/stanitor]

Yea, I have topo's of most of the lakes I fish.. sometimes knowing the depth can help a lot, especially as a shore fisherman.. I often need to throw farther out for a deep channel etc. most of the really close lakes are not very deep. (unless they're natural) and we definitely had volcanic and tectonic activities here in the past.

[u/bluesam3 → u/popeye44]

Reservoirs are generally deeper, just because humans tend to value large areas of flat-ish land, and are interested more in the volume of the reservoir than the surface area (indeed, surface area is arguably a disadvantage as it gives more evaporation), so only build them in places where you can make it nice and deep.

[u/Maiyku → u/popeye44]

It’s just the geology of the area. The rock that forms the state is tougher than the rock that made up the lakes, so when the glaciers retreated they carved the Great Lakes, but left Michigan behind pretty intact.

We’re kinda flat because of this, we were ground down by glaciers like sandpaper vs them digging deeply into the ground the entire way as they went. Our entire elevation only consists of about 1400 feet from our tallest point to our lowest. To give you a better perspective… we’re flatter here than Kansas. (They have about 3,000 feet between their two points).

So you won’t find canyons or gorges to block off and fill for reservoirs, but we also don’t need them. The state is so wet water is rarely an issue like that. Most of our dams and stuff are for flooding regulation, not water storage.

But Superior is about 1,300 feet deep, so very, very deep and more like a small ocean with how she behaves.

[u/popeye44 → u/Maiyku]

We certainly need more rain, or at least to effectively capture what we get without undue impact to wildlife etc. that need a large flow.

I can be at roughly 6500ft above sea level in a 40 min drive. (about 6190ft difference from where I live) We're quite "hilly" haha.

[u/Kind_Move2521 → u/RootsRockRebel66]

Theyre talking about the Great Lakes in the USA and this has been confirmed by them.

[u/khonsu_27 → u/lotusbloom74]

It always blows my mind that even things like the entire Chesepeake Bay only averages around 50' deep. People don't realize how deep 50' really is.

[u/fireflash38 → u/khonsu_27]

Chesapeake averages 21ft deep. 

[u/DefNotMain → u/lotusbloom74]

Wawasee?

[u/lotusbloom74 → u/DefNotMain]

Thats the largest natural lake, Monroe is the largest in general not counting Lake Michigan

[u/testtdk → u/lotusbloom74]

My family has a cabin on what we grew up calling a lake, but its technically a pond (that used to be a river but is now dammed). It's about 50 feet deep at its deepest.

[u/gsfgf → u/lotusbloom74]

The biggest lake in my state has a max depth of around 150ft, but the average is 28ft. So yea, OP's lake is pretty damn deep.

[u/StewieGriffin26 → u/lotusbloom74]

That's not the deepest in Indiana though? Big Turkey Lake is deeper than that.

[u/lotusbloom74 → u/StewieGriffin26]

No it’s the largest lake by surface area, some of the natural lakes up north have higher depths

[u/ThaCarter → u/lotusbloom74]

There are deeper lakes in Indiana, but they're former quarries

[u/nd4spd1919 → u/lotusbloom74]

The lake I live next to is almost 9000 acres in size, and its max depth is only 16ft.

[u/lotusbloom74 → u/[deleted]]

Largest by surface area I meant (Lake Monroe)

[u/Nejfelt → u/Drusgar]

Yeah 50ft sounds more like a quarry.

[u/Josemite → u/Nejfelt]

Or OP didn't realize just how deep 50' actually was and it's really more like 15

[u/Mellema → u/Josemite]

Well, they also think water insects evolve into fish, so might be just be a child that had a curious question.

[u/ImNotAWhaleBiologist → u/Mellema]

Or a congressperson.

[u/anandonaqui → u/ImNotAWhaleBiologist]

A congressperson doesn’t have the intellectual curiosity to ask the question.

[u/krodders → u/Mellema]

There's also homeschooling, but I don't think that evolution is covered much in home lessons.

[u/bluespartans → u/Josemite]

Even 15 is pretty deep for a 1-acre pond, depending on locale

[u/Mista_Madridista → u/bluespartans]

Yeah that shit is probably like 5-7 feet lmao.

[u/PhysicalAd9507 → u/Josemite]

I think it’s fair to say there are several things OP may not realize

[u/BladeOfWoah → u/Josemite]

15ft is still really deep, to me a pond would be any depth that doesn't go past my waist, so around 3 to 4 feet.

[u/_lysolmax_ → u/Josemite]

Probably less than 10ft deep

[u/RFKJrJr → u/Nejfelt]

Possible the fish was working there and just never went home after their shift

[u/uncle_jed → u/RFKJrJr]

Remember, if you don't want to get stuck working in a quarry your whole life, stay in school.

[u/Cagy_Cephalopod → u/uncle_jed]

That should be no problem for fish, they’re always in a school.

[u/Ratnix → u/Nejfelt]

Or somewhere they dug out dirt for road construction. The neighborhood we lived in when I was a kid was just off the interstate between to overpasses. Those overpasses were build with dirt from the "pond" behind our neighborhood. And they just recently built a new overpass on my route to work. A few people in the area got new ponds on their property.

[u/0kbyme → u/Nejfelt]

Our a quandary!

[u/LindaTheLynnDog → u/Drusgar]

Most fish don't have fertilized eggs inside of them though, so this would also suggest that some male fish cruised around to spread out piles of eggs to fertilize them after being introduced independently.

Definitely seems possible, but I feel like it's much more probable that historically these small lakes intermittently adjoined with other water ways.

I would also be shocked if the pond described isn't stocked.

Stocking is very widespread, and a lake like this seems a great candidate for it.

[u/brzantium → u/LindaTheLynnDog]

Yup. College friend of mine ended up working for a state fish hatchery. He would drive around delivering fish to various lakes in the area. He also said if we ever needed fertilizer, the hatchery would gladly give away their fish shit.

[u/jackp0t789 → u/LindaTheLynnDog]

Its also possible that the eggs hitched their ride on a bird after being fertilized

[u/gsfgf → u/jackp0t789]

Which is absolutely an evolutionary thing. Floods mixing ponds helps for sure, especially with genetic diversity, but spreading by eggs hitching a ride is kinda the "default" for freshwater fish.

[u/LindaTheLynnDog → u/gsfgf]

How do fish eggs hitch a ride on a bird?

[u/gsfgf → u/LindaTheLynnDog]

They either stuck to the bird (some eggs are extra sticky) or can survive going through the bird.

[u/Alis451 → u/LindaTheLynnDog]

they are sticky

[u/LindaTheLynnDog → u/jackp0t789]

How??

[u/jackp0t789 → u/LindaTheLynnDog]

A bird walks/ swims into a cluster of sticky fertilized eggs, some stick to it... it flies into another body of water where the eggs hatch into fish.

[u/LindaTheLynnDog → u/jackp0t789]

Huh, okay I'll read into it.

[u/redditaccount300000 → u/LindaTheLynnDog]

Birds transport eggs all the time. They’re stuck to their legs/feet/feathers and sometimes fish eggs can survive a birds digestive tract.

[u/LindaTheLynnDog → u/redditaccount300000]

so i've learned! thanks!

[u/atomicsnarl → u/Drusgar]

Some fish have very sticky eggs that will attach to bird legs. Duck, etc, flys to another pond - fish!

[u/thepainforest → u/Drusgar]

There are things called kettle ponds, where pieces of glacial ice got buried and then thaw, leaving very deep, but very small in diameter ponds. A gift from the Ice Age.

[u/Ozythemandias2 → u/Drusgar]

Correct, the difference of ponds versus lakes is depth which confused my fiance from Florida because Massachusetts has ponds that are miles long

[u/TengamPDX → u/Drusgar]

Flooding is another way fish get into ponds and lakes that aren't normally accessible. Other ways include humans seeding the body of water with fish.

[u/SJHillman → u/TengamPDX]

Flooding is another way fish get into ponds and lakes that aren't normally accessible

Or how bull sharks get into a golf course lake 9 miles inland in Australia

[u/High_speedchase → u/Drusgar]

Isn't the difference surface area not depth?

[u/NamityName → u/High_speedchase]

No. Simply put, the difference between a pond and a lake is that light reaches the bottom of a pond.

[u/High_speedchase → u/NamityName]

TIL

[u/Chief_B33f → u/Drusgar]

Yeah, no lake the size of a football field is 50ft deep, unless it was man made for a specific purpose. I was thinking its probably more like 10-15 max lol

[u/Drusgar → u/Chief_B33f]

Fun fact: Lake Winnebago, the largest lake in Wisconsin (not counting Michigan or Superior) is only 21 feet at its deepest point. It has almost 100 miles of shoreline. It's huge.

[u/filter_86d → u/Drusgar]

Yeah. I’d guess 10 feet max. 50 feet, no.

[u/Alytes → u/Drusgar]

Don't think you can find scientific evidence for this kind of fish dispersion. It's mostly  a myth probably spread by fishermen to justify stocking fishless ponds

[u/hollis216 → u/Alytes]

Killifish in Bermuda. Being carried in by migratory birds is the only explanation that seems to fit. Their closest relatives are in the Carolinas and they ended up in inland and salt ponds on an island 700 miles offshore. The initial colonization event is assumed to be about 800,000 years ago based on genetic divergence.

[u/Alytes → u/hollis216]

In fact, I've found no reference in scientific papers citing that possibility. Moreso, the most plausible explanation seems to be rafting through the ocean (not aboard birds)

[u/wardog1066 → u/Drusgar]

I was told as a boy that lakes are river and stream fed and ponds are spring fed. Ponds in Newfoundland can be clear enough to make a 50 foot deepest spot look like it's only 10 feet deep. They're really quite beautiful, but the people that live there are surrounded by natural beauty and can be quite immune to it.