remove blur effect on child element

Solution 1:

Create a div inside content & give bg image & blur effect to it. & give it z-index less the the opacity div, something like this.

<div class="content">
    <div class="overlay"></div>
    <div class="opacity">
        <div class="image">
            <img src="images/zwemmen.png" alt="" />
        </div>
        <div class="info">
             a div wih all sort of information
        </div>
    </div>
</div>

Use Css

.content{
    float: left;
    width: 100%;
}

.content .overlay{
    background-image: url('images/zwemmen.png');
    height: 501px;
    -webkit-filter: blur(3px);
    -moz-filter: blur(3px);
    -o-filter: blur(3px);
    -ms-filter: blur(3px);
    filter: blur(3px);
    z-index:0;
}

.opacity{
    background-color: rgba(5,98,127,0.9);
    height:100%;
    overflow:hidden;
    position:relative;
    z-index:10;
}

Solution 2:

Add an overlay something like this:

<div class="overlay"></div>

Then:

.overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  backdrop-filter: blur(2px) sepia(50%);
  z-index: 9999999999999999999;
}

Here the parent child relationship is not what matters. The z-index is important.

It will apply the filter to anything sitting behind the div.