Summer's heat is a "thin ice" situation for the intensive pond hobbyist. When you have a collection of fish in warm water, the only thing keeping them alive is gas exchange (oxygenation) at the water's surface. So, you see that the continued operation of your pumps is all that stands between you and 'loss'. Now, folks might note that oxygenation isn't a problem for them, they have live plants and these make lots of oxygen, and they are right half the time. At night, many people are unaware that the respiration of the plants reverses and the plants consume oxygen! So, in summer, ensuring an impenetrable supply chain of water flow is essential.

 In winter, the risks are "two way". First, there's dangerous "supercooling" of the fish by running waterfalls and other surface disruption techniques at night. We discussed this above in the section on water falls.

 The second problem is essentially the basic "chilling" of the fish. Chilling of fish in winter to near-freezing temperatures is extremely stressful to them. Carp are not native to temperate climates by origin. They simply "survive" our winters, but that doesn't mean they're adapted to it. Not only does near-freezing of fish annihilate their immune response, but it damages certain internal organ systems as well. In studies done by several Universities with fisheries departments, they found one of the most common ways that Aeromonas bacteria get into the fish in order to kill them was through the intestines! They showed that fish commonly suffer damage to the lining of the intestines when subjected to near-freezing water; and the Aeromonas uses this area of trauma to enter the fishes' bodies. This partially explains the fact that Springtime is a common time of year for the majority of fish hobbyists to have health troubles with their fish. On the other hand, people whose ponds are heated all winter do not have a "Springtime" disease season. A great deal of technology exists to support water temperatures in winter.

Oh, Those Pesky Herons! An Article on Herons and Heron Control

Koi Beginner
Once you've leapfrogged through this tutorial you will have a solid, working concept of the Koi hobby and what it's all about. This is done just about exclusively with video and very little written material.

DrJohnson.com
More than koi health, this site spans all things animal, by a real veterinarian who shoots you straight.

Fishdoc.co.uk
By Frank Prince-Iles. A UK authority who put this site together some time ago and which is still relied upon as a major source of good Koi and pond fish information

Fish Medicines
Learn about fish medicines, what they do, and where to get them.

PondCrisis.com
If you have a koi, pond or fish problem, this site takes you through twenty easy questions and at the end you know what you need to fix in your pond to create restored Koi health.

KoiCrisis.com
Koi Crisis has a symptoms chart by system you can choose the symptom by fish part, and resolve a lot of Koi pond fish problems or at least, learn about them understand how to remedy them.

Buying Domestic Koi
What does "Domestic" koi mean? Why would you buy that kind? How do you pick good and healthy ones? Who sells them and where do you find the best ones?

Buying Imported Koi
A Japanese or Israeli imported Koi is a beautiful thing. Why would you buy one of those? How do you identify a "good one"? And what kinds are there? Who would you buy one from?

Koi Filtration - Bead
With a little bit of management every week or so, you can have gin clear water in your koi or fish pond. Bead filtration is more than ten years old and defines the state of the art in Koi and pond fish ponds.

Koi Filtration - Natural
Requiring no weekly management but one big yearly overhaul, natural filtration is the easiest there is. Relying on live plants and organic processes, water quality is usually superb. Described and common mistakes illustrated, visit this site!

Koi Food & Feeding
What should you feed your koi? How many times per day? Is Corn really that bad in a Koi diet? What are the most common feeding mistakes people make? What's the best food?

Koi and Pond Hard Goods
So many places these days, are pure ripoffs. Finding a reputable dealer of koi and pond hard goods isn't as easy as you would think but there's ways to tell. The product line should be to-the-point and not contain shams. Who's doing it right? Visit this site!

Koivet.com

Finding Reputable Dealers
The fish are only as good as the dealer holding them. Quarantines, guarantees and fish quality all factor in. What to ask, what to see and how to handle your new fish.

Books on Koi Diseases
You will be introduced to Dr Johnson's Koi Health book but also to other books he's reviewed.

Help With Koi Problems
Koi Community rates a variety of forums and message boards on ease of use, friendliness and quality of help. Not all boards are created equal. Not mincing words here.