There are a number of banks that pay dividends worth considering, but it also turns out there is one big bank dividend stock that should be avoided.

The big dividend
At first glance, Banco Santander (NYSE:SAN) is one of the most attractive big bank dividend stocks out there. Its lofty nearly 8% dividend payout ratio is more than triple that of the average 2.6% yield posted by the 30 other banks across the globe that are currently worth more than $50 billion on the market, according to S&P Capital IQ.

Yet even despite this impressive dividend, there are three reasons I wouldn't consider investing in this bank.

Massive currency fluctuations
One of the first things that caused me a bit of hesitation for the bank headquartered in Spain is the massive effect currency fluctuations can have on its operating results. A simple glance at its reported net operating income through the first half of 2014 reveals just how dramatic this can be: 

Avoid This
Source: Company Investor Relations.

As you can see, thanks to its truly global operations and swings in the relative value of currency, on a reported basis, it saw its operating income decline by 4.9%. But on a constant basis -- which excludes for these fluctuations in exchange rates -- its results were actually up 4.9%.

And this 180 degree swing is a difference of 1.1 billion euros available to shareholders. Such a dramatic impact entirely outside of Santander's control is a cause of concern for me.

Troubling trends in exposure
In addition to the massive impact currency fluctuations can have on its bottom line, Banco Santander also faces the reality that even on a constant basis, its non-performing loans have grown dramatically since the beginning of 2013 and were actually up again -- albeit marginally -- in the most recent quarter:

Avoid This
Source: Company Investor Relations.

And the company notes its ratio of non-performing loans in Spain has actually grown from 5.75% at the end of June 2013 to 7.59% at the end of the most recent quarter. Knowing its loans in Spain represented more than 20% of its total customer loans, that reality is also troubling.

All of this is to say, there are a number of trends that cause concern as it relates to the possible risks that may face Santander.

Lofty valuation
And if all that wasn't enough, it must be mentioned that Santander currently trades at a lofty valuation, with a price-to-tangible book value of 2.0. This essentially gauges the relative value of what the market says a company is worth versus what it would be worth if all of its assets were sold and its debt was paid off.

But the thing is, this P/TBV of 2.0 is well above the 30 megabank industry average of 1.5, and is nearly identical to highly esteemed banks like Wells Fargo (NYSE:WFC), versus those like Citigroup (NYSE:C) and Bank of America (NYSE:BAC):

Bank

P/TBV

Wells Fargo

2.0

Banco Santander

2.0

Bank of America

1.2

Citigroup

0.9

Source: S&P Capital IQ.

And the trouble is, its performance doesn't match this lofty valuation relative to a peer like Wells Fargo:

Bank

Return on Assets

Return on Equity

Wells Fargo

1.5%

13.9%

Banco Santander

0.6%

6.6%

First half of 2014. Source: Company Investor Relations.

The Foolish bottom line
At first glance, the lofty 8% dividend yield offered by Santander immediately leaps off the page when considering big bank dividends. But the reality is, there are a number of things that raise red flags, and it isn't one I would consider an investment in.

Patrick Morris owns shares of Bank of America. The Motley Fool recommends Bank of America and Wells Fargo. The Motley Fool owns shares of Bank of America, Citigroup, and Wells Fargo. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.