Lake devoid of smaller aquatic life

[philocalist]

Just throwing this out to see if anyone has any immediate thoughts / ideas?

Been mucking around over a couple of weeks at a lake newly acquired by a friend - nothing too ostentatious - about 4 acres set in a typical parkland type surroundings - grassland, bankside trees along one edge, and aquatic plants seem to be doing well with a good selection of healthy looking marginal plants - several patches of the typical big white lilys found everywhere, and some patches of that little yellow pygmy stuff too ... and it is because we've been in the water, doing some serious gardening in and around the lake, that we've noticed something that may - or may not - be a problem.

 

Fish species in there are the usual suspects: a couple of carp above 20lbs, maybe a couple of dozen more that are typically around 5 - 8lbs in weight. Bream and tench currently seem to top out at around 7lbs and there is a healthy population of what appear to be mostly smaller roach, rudd and perch .. and some monsterous eels! There is a typical attendance of ducks etc that get regularly bombarded with bread from toddlers, and no obvious issues with predation from otters, cormorants etc - and the place may have seen as many as a half dozen anglers this year!

 

What is puzzling is what seems to be a complete, total absence of aquatic life, apart from the fish and a large freshwater mussel bed that we found ... no detectable presence of bloodworm, and despite all of the raking / cutting and removal of several hundredweight of assorted aquatic plants (both marginal and the lilys), we've seen not one single snail - literally - nor any sign whatsoever of all the insect life and assorted creepy-crawlies that and sellf-respecting 4 year old should be able to haul out in numbers using a 99p net! There is SOME surface insect life ... apart from that - other than the bread that gets past the ducks - we've no idea whatsoever what the fish population is feeding on, though whatever fish that have been caught all seem healthy enough.

 

Water parameters, DO, pH etc all check out as perfectly normal, with no indication at all of anything obviously suspicious ... It's weird, and a first for me in all my years of angling - an apparently otherwise healthy lake with a good resident fish population that appears to be quite literally completely devoid of ALL aquatic life other than fish and mussels ... could not even easily find daphnia etc!

 

We've spent two weeks head scratching without coming up with any answers ... anyone have any thoughts on this?

Edited August 21, 2016 by philocalist

[chesters1]

My pond is the same ,on removing weed theres absolutely no life on it but a thriving mussel population (and cray fish) ,strangely you would think the fish would be starving but its a hard pond to fish .

The fish themselves seem to be fine but very slow growing the resident koi do not have appeared to grown bigger all the time they have been in there.

The fish are not emaciated and apart from sunny days hardly any anglers fish the place ,perhaps the fish/available food is spot on but not enough for growth?

Little surface food either and few dragon flies as well ,lots of ducks but hungry enough to dive 6ft onto baits with the usual. Consequences

 

Strangely theres been a big decline in rudd what was a fish in pest proportions is now quite rare ,you could see the pond as a mass of black on a hot evening but now nothing ,no bodies show up its very strange ,few gudgeon either that once were common

Edited August 21, 2016 by chesters1

[Ken L]

Where does the water source originate?

Any sheep farming in the area?

[BoldBear]

This may not be relevant; I'm not sure; but the park lake in St. Albans has just been diagnosed with too many nutrients and loss of oxygen much of which could have been caused by the water bird population and hundreds of humans feeding them with bread etc. over the years.

 

Do you think you might be experiencing very early signs of this sort of thing?

Have you tested the oxygen and nutrient levels?

 

https://stalbans.gov.uk/council-and-democracy/press-room/items/2015/november/2015-11-10-solution-for-verulamium-park-lakes.aspx

 

Keith

Edited August 21, 2016 by BoldBear

[philocalist]

My pond is the same ,on removing weed theres absolutely no life on it but a thriving mussel population (and cray fish) ,strangely you would think the fish would be starving but its a hard pond to fish .

The fish themselves seem to be fine but very slow growing the resident koi do not have appeared to grown bigger all the time they have been in there.

The fish are not emaciated and apart from sunny days hardly any anglers fish the place ,perhaps the fish/available food is spot on but not enough for growth?

Little surface food either and few dragon flies as well ,lots of ducks but hungry enough to dive 6ft onto baits with the usual. Consequences

 

Strangely theres been a big decline in rudd what was a fish in pest proportions is now quite rare ,you could see the pond as a mass of black on a hot evening but now nothing ,no bodies show up its very strange ,few gudgeon either that once were common

 

Chesters - I could have added your post, word for word, to my original info ... it's spot-on :-)

[philocalist]

Where does the water source originate?

Any sheep farming in the area?

 

 

Water input is surface water only, running off (untreated) parkland grass. Wider surroundings are limited housing about a half mile or more in one direction, an adjacent river, downhill and along one of the longer banks. The other longer bank is woodland for maybe a half mile onto rural fields, usually with crops or fallow but nearest sheep are likely at least five miles away ... it's horses mostly locally :-) ... the final bank just leads off into woodlands that eventually reach a country pub after about 45 minuites of walking.

[philocalist]

This may not be relevant; I'm not sure; but the park lake in St. Albans has just been diagnosed with too many nutrients and loss of oxygen much of which could have been caused by the water bird population and hundreds of humans feeding them with bread etc. over the years.

 

Do you think you might be experiencing very early signs of this sort of thing?

Have you tested the oxygen and nutrient levels?

 

https://stalbans.gov.uk/council-and-democracy/press-room/items/2015/november/2015-11-10-solution-for-verulamium-park-lakes.aspx

 

Keith

 

No reason to suspect that the water is particularly rich in nutrients, and dissolved oxygen levels are good, having been measured throughout 24 hour periods, in open water, around lily coverage etc - there are aerators in the lake already (mostly as a preventative measure to prevent freezing as the lake is not too deep), though they are currently not needed and therefor have been off for months.

pH around the lake is sat firmly at 7, apart from a very slight rise to maybe 7.3 where the pigmy lillies have / had total coverage, during the daytime. Water is generally clear, and can become very clear in the absence of wind. Chemically, I'd be quite happy to get the results in my fish tanks :-) Zero ammonia, NO2 stands at somewhere below 0.5, NO3 somewhere below 0.20, with GH and KH showing at 60 and 120 respectively, the only slight variation there being (again) amongst the lillys.

 

In part, this is what I'm finding so weird ... everything is apparently ticking over very nicely, so what explains the total, complete absence of snails, beetles and other aquatic bits and pieces?

[Ken L]

Don't know.

Organophosphates would have been my first guess but you've ruled out sheep dip.

Low levels of nutrients seems unlikely in a park - especially if people are feeding the birdies.

You say it's clear - you haven't got zebra/qagga mussels filtering out all the suspended algae have you?

[philocalist]

Don't know.

Organophosphates would have been my first guess but you've ruled out sheep dip.

Low levels of nutrients seems unlikely in a park - especially if people are feeding the birdies.

You say it's clear - you haven't got zebra/qagga mussels filtering out all the suspended algae have you?

Nope, just a couple of colonies of large, healthy common-or-garden variety indiginous freshwater mussels - smaller sizes there too would indicate ongoing production and growth, with a few stragglers dotted around the lake.

[Phone]

Philo,

 

Interesting dilemma. How about the surrounding landscape? Not sure what SHOULD be there but over here I'd be looking for lob worms, grasshoppers, various and sundry leaf eaters, mossys, etc. You say the plant life about the bank is healthy, how about back 4 or 5 meters? Do you know if algae is ever a problem? I.e. big swings in water colour. If not DO could it be photosynthetic capacity? How solid is the bottom? Can you or has anyone seen fry feeding in the margins?

 

The identified "problem" is nearly impossible - yet I believe you.

 

Phone