The Green Menace _ When Will It Be Gone?

Cladophora _ pretty at a distance, ugly up close

ROCK snot, the green menace, salad, the guide’s curse, rabbit food and a host of less polite names _ the luminous green algae carpeting the bottom of the White River from State Park on downstream has been a hot topic of discussion.

According to AGFC trout biologist Jeff Williams the nasty stuff fouling lines and flies is Cladophora a common filamentous algae in these parts. It preferred habitat is cobble or bedrock, and thrives in clear water between 59-77F and in higher sustained flows.

The bad news is there is no way to control or remove it. The good news, according to Jeff is Cladophora mostly commonly blooms heavily in the spring and dies off in the summer.

I do not think that this will be continued problem or require anglers to change tactics for the long term.  Given the importance of these fisheries to a lot of people anything that has the potential to negatively impact them is a concern.  However, I think this will run its course in a relatively short time. 

The Journal went to AGFC trout biologist Jeff Williams, with a list of questions, some as blunt as a former tabloid journalist can dream up at 6am fuelled on bright coffee. As usual when we have done this before Jeff took them on the chin and answered straight up what the AGFC knows and what is conjecture, and clearly differentiating the two.

In other comments Mr Williams said:

  • His investigations didn’t point to unusually high nutrient inputs (like chicken litter or sewage).
  • He suspected high water was part of the puzzle behind the this year’s heavy bloom.
  • It was possible the decline in Didymo levels allowed the Cladophora bloom.
  • Lower levels of didymo may have led to the heavy caddis and mayfly hatches this spring.
  • Invetrebrates will feed on Cladophora and it will serve as habitat, but makes it harder for the trout to find them.
  • Trout appear to be doing well despite the bloom.

Read the full text, edited only for relevance, on the click through:

A brown trout swims over Cladophora at Wildcat

 

The majority of what folks are seeing is Cladophora…a common filamentous green algae.  It is not an invasive species like Didymo.  From my observations I definitely think it is more prevalent this year than I can recall.  Exactly why it is more prevalent this year is a little hard to say.

 When we first started getting reports of it there was a concern that the river was receiving excessive nutrient input from somewhere (chicken litter, untreated sewage, etc.).  However, after talking with ADEQ and taking a look at some of the nutrient data from them I did not see anything out of the ordinary. 

This can be a bit deceiving as the algae and other vegetation can quickly take up any available nutrients.  It might also be that the reduced abundance of Didymo (as a result of the high water) has freed up some nutrients for the Cladophora to utilize.

 As an aside, the reduced abundance of Didymo may have played a role in some of the hatches that we saw earlier this year.  Studies have shown that when Didymo is heavy there is a general shift from mayfly or caddis fly species to more midges.  Now that Didymo is cut back (but not gone for good) the mayflies and caddis flies may be doing better.

Caldophora generally requires a hard substrate such as cobble or bedrock.  It is usually found in water temperatures of 59-77 degrees F.  It thrives in clear water where sun light can penetrate and we definitely have that here.  Additional nutrient inputs (especially phosphorus in freshwater) can stimulate Cladophora production, but heavy blooms of Cladophora have been observed in the absence of additional inputs. 

Although heavy flooding can scour Cladophora, somewhat higher sustained flows have been observed to result in increased production.  Given this I suspect that higher water that we have seen in the last couple of years may be part of the puzzle.  Not only do the sustained flows continually provide the algae with the materials it needs for growth, it also allows it to become better established in the channel margins that are dewatered less frequently.

Invertebrates will feed on the Cladophora and it can also serve as habitat for them.  From my observations the bugs and other food items for trout generally do well in the Cladophora, although it can make it more difficult for the trout (especially the rainbows) to get at them. 

Based on reports from anglers and my own observations, the trout appear to be doing well.  I think the biggest impact so far is to the anglers as the stuff can foul their lines.

 Cladophora commonly blooms heavy in the spring and dies off in the summer so I do not think that this will be continued problem or require anglers to change tactics for the long term.  Given the importance of these fisheries to a lot of people anything that has the potential to negatively impact them is a concern.  However, I think this will run its course in a relatively short time. 

 As far as actions, I think that our best course of action is to continue to monitor for the next couple of months and hope we see it start to die back.  I think education is a big one in just letting the public know what it is and what it is not.  

 There is no viable option for chemical or mechanical control/removal.

2 comments

  • Frankly l would rather have to deal with the algae than didymo.
    I am not so sure the decline of the didmo has anything to do with this as this incidence is way further downstream than the worst case scenario when didmo carpeted the river bed which was 4 years back at its worst.
    I believe also the high water we have seen for the past few years has also been largely responsible for the increased bug activity we have seen this year, granted there may be some increase due to the decline of didy for the upper 12 miles of the river.
    No question of doubt the fish are in great shape, pretty much lost count of the 20 incher Bows at the upper end and as we all know the overall increased size of Browns and Cutts in the system.
    Which would not be the case if we had seen low water for the past two years and neither would we have seen the caddis emergence of this year either.

    DW

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