Swimming headache

It very well may be lack of oxygen, but it also may be that you are getting dehydrated.  Even though you are in the pool, you still sweat.  Keep a water bottle nearby and drink regularly.  Another possibility may be incorrect stroke mechanics.  Typically, if there is alot of "thrashing" in the water, that gives people headaches too.  All three are a possibility. 

Are you wearing a swim cap? Mine sometimes gives me a headache so mid-swim I will take it off and do a few laps without it, then put it on again later. Also, your pool might be too warm. My gym pool has raised their temperature just a degree or 2 but it makes it impossible to do long swims without getting overheated which gives me headaches.

I was getting very bad headaches while I swam as well. My first reaction was , I must be dehydrated, but hydration wasn't the problem. When I swim I breathe every second stroke, so I am always turning my head the same way, same as you, if your breathing every four strokes. It caused me to get a pulled muscle in my neck, which resulted in me getting headaches. I saw a doctor and he gave me some stretches and I am now swimming headache free.

I used to get them for two reasons, dehydration and my goggles were on too tight.  Make sure to stretch lots too.

I had the same experience the other day and I think mine was lack of O2.  I have gotten the same headaches during SCUBA and it was definitely due to short, choppy breathing.  Try to not only take good, long breathes but also deep breathes.  Even if you have to slow your pace a bit.  Make sure you exhale all the air in your lungs then breath deep into you stomach.  This has helped me immensely in all three areas of tri.  Also, breathing every 3rd stroke has really helped me. 

1. breathing every 4 strokes means you are probably low on oxygen if you are swimming hard!
2. you are stressing your neck anatomy by only turning one way...should try to learn bilateral breathing...it WILL help.
3. drink, I agree
4. flip turns sometimes give me a headache, so I vary my wall turn methods
5. goggles/cap too tight?
6. try to remain calm in the water, even if it means swimming painfully slowly until you find a pace that means you aren't suffering afterwards.
7. stretching, I agree.

I still get "foggy - brained" after hard workouts but I know it will pass..it doesn't stay with me anymore, like it used to.
Hang in there and keep plunking away

please define ... hypercapnic vs hypoxic...

Hypercapnia is an increase of your CO2 level from poor overall ventilation (not breathing deep enough or exhaling well).  Hypoxia is a decrease in your oxygen levels.  I believe what is being said by the previous statement is you need to remember to exhale as well as brethe deeply.

Thank you for clarification...that was very helpful and something I will remember while in the h2o
Thx

Another thing to think about is your jaw, do you think you might be clenching it?

Just something to think about.

I was having a lot of trouble with this as well up until last November. I tried just about everything suggested here (hydrating more, not doing flip turns, loosening my goggles, etc) but nothing worked. I started using the Neti Pot for my allergy/sinus issues in November and since then I have not had a single headache due to swimming. I totally think my issue was my sinuses.

I'm not sure if you have a history of trouble in that area or not, but if nothing else works it might be something to consider.

I have had headaches from swimming in the past but just last week I had an unusually intense headache after a 2000 yard swim. It lasted the rest of the day. Ever since then it seems that the headache has never fully gone away. Even when I can't really feel anything it seems it is lying there dormant ready to start hurting again. A few days after that long swim I did an OWS that I had to cut short because I felt the headache coming on again. I got out of the lake and put my running shoes on and the headache seemed to go away. It has been four days since the first long swim when I noticed this headache. There has maybe been one day out of the four where I haven't had a headache. I have been drinking plenty of water throughout the days. I also haven't changed anything in my training so I'm not sure where this is coming from. Any suggestions?