two ways of getting this result are running the gel at too high a current so heating the gel and buffer too much and causing smearing of the ladder. Also re using old buffer in the gel tank. It can gave bacteria growing in the buffer which enzymatically degrade the dna of the ladder ( it degrades the dna samples too but this looks less obvious) so use fresh running buffer.

I agree with Paul Rutland, those are likely sources of the smear you see instead of nice bands. Is anyone else running DNA gels and seeing similar results?

Another possibility is accidentally using low melting point agarose instead of standard agarose and having your gel soften in standard running conditions.

Paul Rutland thanks for the respond, do you think the fluctuation of the wire in the volt could lead this, because we on shared bench and people might accidentally shake the bench while they are setting up other assays.

If other people are ising tube shakers like whirlymix while the sample is loading and still in the gelI think that it might lead to blurred bands but once the dna is in the gel it will be held in place by the gel matrix but I am still thinking that it is a dna degradation effect for 2 reasons

1 the dna ladder is not shouwing as clear , sharp bands and

2 most of the southerns that I have run show the enzyme cut dna as starting narrow like the well then looking curved and bright then at smaller sizes looking straight edged and less bright. This effect with 2 slightly curved sides is caused bay longer dna taking up more EtBr so looking brighter than the less common very large fragments but the shorter dna intercalating less EtBr so looking fainter but your tracks look parallel sided which may be caused by randim nucleases degrading the stronger absorbing larger fragments