Not all oxygen producing water plants are big enough to get tangled on your fish hook. Most oxygen production in pond/lake by plant photosynthesis is primarily by microalgae that is basically invisible as single plants suspended in the water column. Usually tens to hundreds of thousands of them PER OUNCE of water!
And just to prove it, Bill was kind enough to do a survey of what I thought was close to 'dead' water in my pond after a sudden weather change last year and what looked to be a complete die-off of my 'bloom'. Here are the results from what appeared to my naked eye to be darn near clear water:
Numbers in cells per milliliter unless noted
CYANOPHYTA - CYANOBACTERIA -Bluegreen algae
Oscillatoria angustissima 23,978
PICOPLANKTON 1-2um dia 1871
CHLOROPHYTA - Green algae
Ankistrodesmus falcatus 346
Ankist. spiralis 554
Carteria sp. 69
Coccoid unicell greens 633
Francia ovalis 69
Pteromonas sp 1178
Treubaria setigera 2287
CRYPTOPHYTA
Cryptomonal erosa 218
CHRYSOPHYTA - Golden brown algae group
Mallamonas sp 2694
MICROFLAGELLATE 69
BACILLARIOPHYTA - Diatoms
Cyclotella 207
Nitzschia acicularis 69
Nitzschia sp 69
Synedra delicatissima 73
Synedra tenera 207
TOTAL CELLS /ML 34,591 or 1,023,894 per ounce
Suspended detrital particles 0.1-1.0 um dia 426,750/ml
Susp. det. part. 1.0-5.0 um dia 133,360/ml
Total Susp. detrital particles 560,110/ml or 16,579,256 per ounce
On a related note: During the blackout a week of so ago I did not have a batery back-up aeration system for two of my indoor minnow tanks, both with about the same density of fish. One tank is filled with tap water and the other with water from my pond. Neither tank has any multi-celled plant life. Both get partial sun each day with the pond water tank having a slight green tinge. The tap water tank, (Exceedingly clear) had an almost complete die-off of the cool water minnows and the other tank had zero loss. The only thing I am able to surmise is that the microalgae in the pond water tank produced enough O2 to keep the fish alive.
