Joseph F Gerrath jfgerrat at
Thu Jul 6 19:54:17 EST 1995

nbf2 at Lehigh.EDU wrote:
: Hello-

: I'm stumped, I have a B.S. in Environmental Marine Science but not too much
: experience in freshwater ecosystems.  There is a pond at my home that used to
: be a mine-hole.  Every year it would purge brown and green algae - typical
: stuff - easily killed off with copper sulfate.  The last two years the purge
: has not occurred but instead a green seed has covered the pond starting in May
: and it dies out in September.  The water is crystal clear under this layer of
: seed, so I have ruled out a tannic acid reaction or form of algae.  I've never
: seen anything like this before.  The color is kelly green and the size is
: about .5 mm in diameter and feels like sand.  We have been skimming it off for
: approx. two hours each day but it doesn't see to be diminishing (either the
: bloom is over and the layer is thinning out or it keeps producing??????)  The
: pond is stocked with catfish, carp, bass, and sonneys.  The carp seem to be
: feeding on this seed but like I said before the quantity of it is not
: decreasing.  The only environmental change in the area is a housing development
: that has been introduced which is about 300 yards from our property.  Another
: kicker is that our pond is not the only one like this, we have seen this seed
: on other ponds in the area anywhere from our house (Whitehall, PA) all the way
: up to Scranton, PA.  Plus, a friend of ours has two ponds on their property
: and one is covered with this seed and the other isn't!!! figure that out!
: That piece of info leads me to believe that it is a water chemistry thing...

: PLEASE EMAIL ME AT NBF2 at LEHIGH.EDU                THANKS!!!!!

:                     Natalie
:                     nbf2 at

I'd be willing to bet that you don't have an alga, but have Wolffia 
columbiana (one of the duckweeds), a flowering plant!  Don't ask me how 
to control it ... that is not my turf.  You should also expect to get it 
every year if it is in the neighborhood because water birds will 
transport it in.

Joe Gerrath
Dept. Of Botany
Univ. of Guelph

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