Is it normal a disgusting number of flies landed on my garden?

Bit of a random post, but anyway, we bought a bag of blood & bone for my garden. I'm a bit of a newbie at gardening, so decided it would be a good idea to pour the remaining contents of the bag just over the top of my garden bed, and around my plants. A couple of hours later, huge population of flies came. No amount of watering gets rid of them. A few days later, I'm absolutely disgusted. This is almost intolerable. Imagine the amount of flies surrounding a corpse, then multiply that by like 3, and that's the amount of flies I see on my garden bed, under the shade cloth. I come near them, they buzz around and go crazy. The air is covered with them.

Omg, what do I do about this situation. Does this usually happen with blood & bone fertiliser? And how do I get rid of these pests.