I see people trying to get the green bubbling pond scum from their ornamental or fish ponds and I understand the reason for that. My situation is a little different
I live on a small ranch in Western Central Colorado, near Glenwood Springs, and build small ponds to help saturate the soil around my yard in Summer and dip water from them to water my container plants and small trees (when I get time to plant them).
We have high mineral / hard water here...lots of sandstone and limestone and granite. This water flows from a hillside into my yard areas and is somehow fed by natural mountain springs that I can't understand how it exists, lol. I think they're fed by snowmelt because only flow April-October.
I acquire bubbly green pond scum on my very small 6-8' diameter ponds that don't have drainage ditches and simply lose their water slowly to the soil around them.
These are the ponds I pull water from with buckets or watering cans. I tend to disturb the water with the container to disburse the scum bubbles and then dip the water out. So far my container plants (beans, tomatoes, herbs, squash, corn, etc) seem to be starting up / sprouting fine from using this water.
From what I gather this stuff is produced by plant matter decaying and high oxygenation. It is healthy water for all stages of plant watering right? It seems to be but I'm novice at this stuff. This is only my third year of gardening and living here.
It's hard to say without a picture, but I'm guessing the scum is an algal bloom. I also water plants from a similar-sized pond with the same issues, and have seen no ill effects. (I've never used it on seedlings, though, just to be on the safe side.) The problem with these blooms is that as algae decays, bacteria can use all the available oxygen, resulting in anaerobic activity - and the chemical byproducts thereof - detrimental to plants. I follow my nose, and never use water that smells stagnant.
Algal blooms shows an excess of nutrients in the water. The water itself is like a compost tea. The algae, however, is absorbing these nutrients into plant matter, making it a good soil conditioner and, thus, would be a good addition to the compost.
My next door farmer neighbor has a pond which is over growing with this stuff. He's raking it onto the banks in bales to dry out and asked me if I was interested in the material for composting or whatever. My initial response was "hell yes!", but now I'm wondering otherwise. His land is farmed conventionally using "roundup ready" seed and of course Roundup for weed control. I'm thinking that the field runoff into the pond is likely causing the algae blooms in the first place. I have no idea about the science behind this. Should I think of this material as likely contaminated or is there likely little or no uptake of nasties in the algae?
If there are bubbles caught under green slimy stuff, then it's algae, and that is not good for the health of critters in that pond because of the lack of oxygen. You want a healthy pond teaming with pond life to stop the mosquitoes, bring in frogs, etc. If there are little newts in the water under the algae, they are poisonous, so don't touch them with bare hands, but they eat mosquitoes, they are part of the ecological balance of things.
If it looks like tiny plant leaves it's probably duckweed. If it starts out green, looks like plant leaves and turns red, it's Azola, both of which are good for composting, but should be scooped off the pond.
Birds are going to bring in plant life on their feet, so no surprise that it's there, and that it will change depending on the weather, or whatever plant is migrating around the state.
I use whatever plants or algae grows on my pond. My pond level has been low the last few years because of the west coast drought, animals came to the shore, pooped on it as they drank, particularly the rabbits, and when it rained again, filled up the pond, the algae went nuts. For 10 weeks we scooped algae off, in several muck buckets per week, and I spread the algae around the perennial berries and fruit trees. A million sow bugs got underneath the algae but didn't bother the plants. This spring everything was doing really well, and several plants I thought were goners came back with real gusto.
I pump straight out of my pond because it is essentially a compost tea container. I use fine filters on the pump end to keep the stuff from getting into the lines.
Don't fall for the My-Place-Is-Special, It-Won't-Happen-Here Syndrome.
TO: Christopher Robbins
FROM: Eric Koperek = firstname.lastname@example.org SUBJECT: "Pond Scum" as Fertilizer
DATE: PM 6:55 Tuesday 21 June 2016
(1) All aquatic plants (even "pond scum" = algae) are good organic mulch and fertilizer.
(2) Apply "aquatic weeds" to crops and soils like you would any other green plant materials.
(3) Aquatic algae and other aquatic weeds may be composted if desired but this is NOT essential.
(4) Aquatic plants used as mulch rot quickly releasing nutrients for crops.
(5) Using aquatic plants for fertilizer is a very old agricultural technology dating back to Egyptian times.
(6) There are many examples of agronomic and horticultural use of aquatic weeds around the world. A good example is the use of aquatic weeds as mulch and fertilizer for chinampas = raised fields in Mexico, Central America, and South America.
(7) Pond water, by itself, may contain substantial quantities of plant nutrients. Irrigation with "green pond water" is a common horticultural practice employed by farmers throughout Southeast Asia. Gardens and orchards are planted around fish ponds to take advantage of nutrient-rich water, aquatic weed mulches, and fertile mud.
( A well managed = well fertilized fish pond will be "pea soup green". Insert your arm down to your elbow in pond water. If you CANNOT see your hand then the water has sufficient nutrients. If you can see your hand then pond needs more fertilizer. Most small farmers raise ducks on their ponds. The ducks eat both broad leaf aquatic weeds and broad leaf land weeds. Duck manure fertilizes pond causing enormous "blooms" of phytoplankton and zooplankton. Stock ponds with various species of carp. For example, silver carp eat plankton, and grass carp eat any kind of plant material (aquatic or land plants). Well managed tropical fish ponds (3 feet deep) produce 5,000 pounds of edible fish per acre each year.
(9) In China and Southeast Asia where most pigs are raised in pens, it is common practice to build pig sheds over shallow fish ponds so pig manure can fertilize water = feed plankton that provide food for edible fish.
(10) Kelp and other marine "seaweeds" also make good fertilizer for fields and raised beds. Farmers in Ireland, Scotland, and the North Sea Islands have been harvesting seaweeds for hundreds of years, mostly to make "lazy beds" for growing potatoes.
(11) In some areas of Northern Scotland & nearby islands there is insufficient land to provide enough forage for sheep. The animals graze on kelp and other seaweeds along the rocky beaches.
(12) Pond scum and pond water are good for plants but NOT good for people. If you must drink pond water, filter the liquid through fine cloth then boil before drinking. "Raw" pond water can make you VERY SICK!
For more information about old-fashioned biological agriculture please visit: www.agriculturesolutions.wordpress.com -or- www.worldagriculturesolutions.com -or- send your questions to: Agriculture Solutions, 413 Cedar Drive, Moon Township, Pennsylvania, 15108 USA -- or -- send an e-mail to: Eric Koperek = email@example.com