Pond Boss Forums Thread Like Summary - Algae and Dying Bluegill ... a connection ?

I have found 3 dead bluegill floating in my pond in the last few days (seldom find dead fish). They are all jumbo size bluegill and may be ones I transferred from a local lake 7 weeks ago to hopefully help add to the forage base............. although not sure because I already did have some fairly good size bluegill in the pond. The Filamentous Algae started about two weeks ago with onset of warm weather and is pretty bad this year - I am now just getting around to spraying it with Mezzine as I have done in the past.

I am puzzled (and anxious) why this is occurring and why only the largest bluegill in the pond are being affected ? Nutrient wise - we had a long spring this year and the Canada Geese that visit during the winter and spring were more numerous and stayed longer than normal, I have 5 grass carp approx. 15 lbs each, and last week I fertilized the lawn surrounding the pond with some 23-4-10 fertilizer.

Because I irrigate the lawn out of the pond, it receives daily approx 6000 gallons of fresh water from a nearby river that is known for being super clean (snow melt - no industrial contaminators).


Pond specs:

20 years old
1/2 acre
11'-12' deepest part
Water temp - measured 3 PM .......... 82.1 F surface and 78.8 F down 3'
Incoming water temp 70-72 F (6000 gallons daily)

So is there a correlation with the Filamentous Algae growth and dying bluegill or ................??

Thoughts on this appreciated.

https://photos.app.goo.gl/Q7PfSoQDr3CwoX4k7

Attached Images

Pond star, Bob will chime in when he has time, but I will try to lead you in an acceptable manner.
First, aeration is best at night in the hottest time of year. We don't want to roll that upper layer of 3-4-5-6" water that is 4-8 degs higher than what's underneath .. #1, the higher the water temp, the less dissolved oxygen it will hold.
Some of the timing on this depends on the output capacity of your aeration system and the efficiency of the diffuser/s.
Some species of fish have different tolerances of D.O., but a solid number to stay above is 4ppm. Higher is better, and to get higher we need to drop the water temp so it can hold more..aerating at night without the day cycle is how we can best do this.
Photosynthesis creates DO as the O2 producing organisms "bloom" during daylight periods. The problem is we heat the water aerating in the daytime and warm water holds even less, so really, we are hurting the oxygen levels by simply rolling warmer water into the mix, or more accurately, moving the cooler water to the surface and effectively warming it.
I'll step out on a limb here and say I believe Bob will say 9pm to 9am on aeration. He will correct me if that's not what he'll recommend.
Nutrient loads and aeration: Aeration will help to some extent by providing DO to deeper levels that allow beneficial bacteria to thrive in what would be normally low or absent DO aera to more likely consume detritus/organic matter and reduce unused nutrients-REDUCE not remove.
As for the algal mats, aeration basically pushes it to the sides of the pond but it really has no other affect on algae. Best thing to do with algae (nutrients locked up) is physically remove it when you can reach it..
I have to back up here... floating algae mats are nutrients that are tied up, it's not a free nutrient, but as it dies/is sprayed, it decomposes and the nutrients are released back into the water in their basic forms which can be used by aquatic plants or form as algae mats again.
As for measuring dissolved oxygen, there are some very expensive digital type meters with probes that can be very accurate but can also be very temperamental. I use a chemical test kit for DO measurements but can only measure to a depth that is the length of your arm. Plenty sufficient in most cases. The La Motte kits are very useful if you follow the guidelines closely.
I hope I've helped answer some of your questions in a manner that makes sense.

Cannot put that water source on a timer currently - so best can do is to turn it on can manually first thing in the morning. River water temp dropped by two degrees today as we got got a haze that set in - and air temp only got to 90 degrees compared to the 100-105 it has been the past few days.

Put in 12,000 gallons of river water and ran the sprinkler for 4.5 hours - so hopefully that is helping along with the air temp drop. No morts found today.

I moved the replies about aerating at night to https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=551612#Post551612 to it's own thread to help anyone in the future that may search for that subject.