Mantua Inquiry

[flyrod1]

Has anyone been to Mantua this week?
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[Dgallen]

We went on Saturday the 4th and it was pretty tough. Fished from 5:30 AM - 12:00 PM and caught a few (literally a few) bluegill and 1 bass. The water was super clear, probably 30-35 feet of visibility along the shoreline and no wind at all. The fish were really spooky. Fooled the gills on a flyrod with a dry fly as an indicator with a zebra midge dropper and found 1 bass on a senko. There were plenty of gills and bass cruising but man alive I've never seen fish so spooky. You'd try to cast past them 30 feet and work it back to them and they'd still hear the splash and take off. Anything with a bobber or strike indicator would scare fish off as it hit the surface.

This has been a weird year for Mantua for us. Usually by now we've boated 10 or so big bass but this year we haven't landed any big ones. The weather hasn't helped out much so maybe it's just that?
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[TheFishSlayer]

I took the kids up there Wed. We spent a few hours on the water. Boated 5 bass and 1 bluegill.
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[Jedidiah]

The indications are that they did some kind of treatment at Mantua last fall without saying anything about it. It's simply been too long without any good days reported and the gills should have been moving up long before now if they were actually still in there. My guess, from comparing the vegetation in there now to last year, is that either the city or some well-meaning freelancer tried to "treat" the weeds and badly over estimated the volume of water in the reservoir. I know it's crazy to think they might have done something like that but it's not the first time that unexplained fishkill has happened at Mantua.
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[AlexB]

I went there once and had a rough time the little time I spent fishing.

However I haven't heard of a kill. You would've heard of reports of lots of dead fish like a few years ago. Also the water level is higher this year than what its been the last few years. Maybe that's why you don't see as many weeds yet. Granted, the water level doesn't change much in Mantua. At least not like other reservoirs.
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[dwayneb]

This past ice fishing season something happened at mantua that changed everything. The first two trips to mantua yielded big perch, gills, and bass. The following trip fishing the same spot the water had turned brown...and we never caught anything apart from a few slimmers all winter...this transition happened the week after the DWR were actively seeking input out on mantua whether anglers were pleased that the DWR had decided not to plant more trout. I went out once this spring using typical drop shot in deeper water for the bass and got nothing...a ate clarity was poor...
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[lavaman]

It wouldn't be the first time. Seems they like to experiment with 'kill offs' every once in a while. About 3 years ago same thing happened...slayed the gills one week, and the next week we go back to see them belly up all over the place. Makes you wonder what they've been doing.

Especially the last year or so, I've noticed (and many others) that the fishing there has gone way downhill.
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[Jedidiah]

AlexB, I appreciate your counterargument because I want to believe the gills will be back but like DwayneB is saying, there has been this uncharacteristic lack of fish ever since the ice season. It's interesting to hear the water clarity changed after the start of the ice season, the lackluster reports started right after the icefishing started. Seems like that would be a good time to do a unscheduled kill off.
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[RockyRaab]

So you guys are saying some unknown agency or person poisoned Mantua through the ice?

Neat trick, that.

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[Fowl-Hook]

Or are they saying WInter Kill, Oxygen deprivation. Invasive disease might also be considered, fungus or something else that spreads.
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[RockyRaab]

You are a much better thinker, dog-lover.

People keep repeating that rumor of chemicals being used at Mantua, but I have never heard of any proof.

Facts: Mantua is heavily weeded. Last year, the water level got very low. After the ice formed, all those weeds died and decomposed.

With the reduced volume of water and ice cover, the oxygen level probably dropped to a level that fish could not tolerate.
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[BagABigOne]

The stocking report indicates that they planted trout in April.
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[Fishsticker]

While I agree that fishing was different this winter than in recent years, fish were still there. I had several bucket filling days with perch and gills. I have a hard time believing that the lake was chemically treated, anyone that dropped a flasher or camera in the shallows (less than 3 feet) this winter should have seen the massive clouds of 2-3" perch.
To the OP no I haven't been there this week but I can guarantee that the lake is ice free.
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[Jedidiah]

You're right Rocky, that's a lot better explanation and pretty likely given the available evidence. The same thing seems to have happened at a favorite bluegill lake of mine that is far too inconsequential and inconvenient to reach to have been poisoned. Low water levels, lots of weeds, weird water clarity after ice-off, and no fish to be seen at all this spring. Not even sure if the YOY survived.
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[scartinez]

Fishing has been pretty standard for me this year. Went on Friday and caught 15 or so bass and tons of bluegills that were on beds.
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[lucky_water_nut]

I don't know what all the fuss is about. I was there Friday and caught 13 bass myself (released all) in like two hours. I was not fishing for bluegill but saw plenty of them caught even from shore. I was using a perch crank bait and could not keep them off.
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[Dgallen]

[quote scartinez]Fishing has been pretty standard for me this year. Went on Friday and caught 15 or so bass and tons of bluegills that were on beds.[/quote]

Nice. Yeah I wasn't hinting towards a mass poisoning that killed off all the fish, just was curious if others were having as a tough a time as me. Usually between the standard weightless plastics fished slow and the standard search baits we can have some really fun days. This year the stars just haven't aligned and it's been tough.

But for the sake of less competition, yes there has been a mass poisoning and all fisherman should spend time on other lakes. And the poison has been left over in the water and will cause swimmer's itch x 10 to any recreational boaters.
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[gstott]

Honestly I think it has more to do with high water scattering the fish and an unsettled spring making them less active. The waters in southern Idaho haven't been as productive overall this spring either, but I think things will be more consistent now that things are warming up. Every year is different it seems.
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[Dgallen]

Agreed.

I emailed the biologist and got this response:

"We did sample Mantua in 2015 and the population of bass and bluegill continued to look good. I'm behind on working up the data and studying the age and growth as we've had some personnel shortages and other large projects come up that were unanticipated, but my visual impression from our sampling was that things looked pretty similar to 2014, with a healthy balance of large and small bass and bluegill. Regarding the fishing and odd water over the winter - I think we've been dealing with some interesting side of effects of changes to water quality over the past several years and that is beginning to have some effects on the fish and fishing. This is just speculation based on what I have seen with the water quality and the results of a concurrent creel survey we conducted at the reservoir last year, so the following are my thoughts:

In normal water years, the reservoir usually gets "flushed" as new and clean inflow water enters the reservoir and the old water that is concentrated with nutrients leaves the reservoir through the outlet pipe and spillway. As of 2015, this hadn't happened in a few years, and what we saw was lower water and more phytoplankton (free floating algae) blooms during late summer due to a build up of nutrients in the reservoir. It seems like around late July of last year we had a large phytoplankton bloom (green water) that took hold and fishing pretty much shut down for the summer after that, as the bloom produced low water clarity and I also think oxygen concentrations were probably lower than optimal due to all the plant respiration from the existing rooted plants and the phytoplankton bloom. This plankton bloom lasted long enough that I think it shaded out a lot the rooted plants in the reservoir, which appeared to have died off during the late season and early winter. This is not a problem in the long term as most of the plants are either perennial or had already produced seeds for the season, but I think the main result of this was little to no cover for the young bluegill this winter. Usually there is some plant life that hangs around during the winter and provides some marginal cover for the young bluegill, but I think this may have been largely absent this winter and that means that the perch, bass, and trout likely had access to all the young bluegill they could eat. With the predators well fed and the young bluegill out of the picture, that meant the adult bluegill should have also had all the aquatic insects to themselves and were thus well fed too. With all the fish having access to plenty of food, its clear the fishing suffered quite a bit. I had colleagues that are excellent fisherman that went out several times this past winter, and while they marked lots of fish on their sonar, it was just very tough fishing. While the water was a bit of an off color during that time too, I don't think it had too much effect on visibility for the fish as they always seemed to show up on the sonar to check out what the anglers were presenting, they just didn't seem too interested in biting. That brings us to this season. From what I've heard, the fishing is just starting to pick up again. I was out for a few hours about three weeks ago and hooked a nice bass, but the water was crystal clear and the fish were definitely pretty easily spooked. I talked with a few other anglers that day and they had caught some bass too, so I think the fishing has just been very hit and miss. I would chalk it up to most of the fish being very well fed this winter, which probably brought them into spring with some good fat reserves, and then it seems we've had some good storms or winds most weeks, which have also made fishing tougher and more unpredictable. I think as we get into summer and the weeds grow back, we should see fishing return to more normal conditions. Hope that helps. Feel free to ask if you have any other questions. Good luck out there."
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[happybob91]

I'm going there tomorrow in my float tube to target some gills with my fly rod, and maybe some bass too. I've heard some folks say it's hot, some saying it's slow, so I guess we'll see how it is tomorrow
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