Why is the lake black?

Never considered it was black but it appears that way. Water can appear man ways depending on what is in it an lighting. Are you suggesting it is a lake of goo?

Reflection of mountains and sky.

Here is an image of Kelimutu Volcano in Indonesia.  Notice one side is green one side is black.  Each side changes colors and they believe it is related to chemical reaction of the volcano gases and the water.

Yea I'm thinking they were going for goo. I know it might just be water. Just thought that since the rumors go that the planet is infected with goo that the algae is too. That's why I asked. You guys are sayin no way? No how?

I always thought it was just the dark shadows of the surrounding mountains as SM pointed out. Imagine a lake of Black Goo, the horror... 

Speaking of H2O and goo, Ridley did mention in a Prometheus interview (back in early 2012) the alarming rate of which bacteria can spread in water in minutes hours and days.

Bacteria and mutations (goo, spores) seem to be a new theme in Alien, and in theory a great addition to the horror aspect of the series. Let's see exactly how the spores and black goo turn out in AC. No more zombies please 

I think its just water... and has that dark shade because of the ambience of the atmosphere.

This is causing me to ponder now. Just how much of this planet has been infected? Are the spores simply self contained in those pods? If they weren't I'd imagine the wind and rain cycle would have spread them across the terrain. If that were the case, shouldn't all plant life including grass and trees be aggressive?

could be black but I doubt it, just the way the light hits it

I was thinking that it's just regular "water" or liquid and the dark color is just a refelection.  But maybe it is infected with the black goo 

This is reminiscent of Prometheus Fire and Stone.In that black goo kind of flowed freely on LV-223,though I'm not sure if there were any lake's of it.

@Neomorph yah you're right, at the beggening of Prometheus the engineer drank the black goo, but the cup also fell in the water... could the be a lake full of black goo from that scene in Prometheus?! That would be scary and cool at the same time.

Fire & Stone had a goo infected lake.

The image above however is just a lake, with mountains reflecting on it.

looks black to me

it could be infected with the goo

I think as SM pointed out its just the shadows at play, but then as Rick Mentioned  his point could also be a explanation.

Also if these Engineers are the would be Gods or those above them are, then surely as part of Tera-forming worlds, and if we look at Biblical Events and other Mythos about God Re-setting the Earth.  Be it like the Great Floods or other means.

Then surely a Black Goo or Xeno would be a bad idea, but maybe if this does not work for what ever purpose they would use such things..

Having a Fail Safe, where they can manipulate the worlds Core and cause massive Magma/Volcanic Activity as the Ultimate Re-set Switch.

This could explain some of the looks of that scene, which would fit with Ricks Kelimutu Volcano in Indonesia post 

Hell it would even explain LV-426,   if the beings above the Engineers have many many Worlds and they are vastly Ancient and can live for a vast amount of time, then in context of their Agenda for Building worlds, if a few would take Hundreds of Thousands of years to then start to reform to a Habitable World, then why not?

Especially of those at the Top of the Hierarchy are beings of Billions of years of age etc, and to a degree Godlike Immortals. (not saying they cant die... much like Vampires i guess then).

But we can maybe still debate the Black Goo element as Fire and Stone had similar lakes... but we cant say this is what has happened.

Right now we dont know to what degree and when, this World had faced anything related to a Black Goo attempted Holocaust

Thank you S.M. i just reread Prometheus Fire and Stone and noticed it this time.

S.M.:Who's to say the lake isn't black?We haven't seen the movie yet.

This landing scene was fairly short and easy to ignore/miss. The more I see it, the more I see that the lake appears black and even the surrounding hills have a gray/black look. Even in an overcast environment, green foliage tends to pop out.