This year has been a challenging one for income investors. Many companies cut or suspended their dividends due to the uncertainty caused by COVID-19. Meanwhile, several other payouts are at risk of those same outcomes if market conditions don't improve. Because of that, they're not great buys right now. However, they're intriguing options for yield-seeking investors to watch. Here are five worth putting on your income watch list.

ONEOK

Natural gas pipeline operator ONEOK (NYSE:OKE) currently yields 12.7%. The payout has risen to such heights partly because investors are worried about its long-term sustainability after the impact this year's oil market downturn had on its cash flow. While ONEOK has no plans to cut its dividend, it might need to go that route if market conditions don't improve, since it could use that cash to pay down debt. Given that uncertainty, investors should watch this dividend stock for now. However, if its leverage ratio and market conditions improve, its payout would become a more attractive option.   

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Energy Transfer

Midstream giant Energy Transfer (NYSE:ET) is in a similar position as ONEOK. It currently yields a sky-high 18.4% because of sustainability concerns. It also doesn't plan to reduce the payout, but might need to if market conditions and its balance sheet don't improve. There's hope for the latter since Energy Transfer's capital spending will decline sharply over the next three years, which should give it excess cash to reduce debt. However, one of the pipelines it operates, Dakota Access, is at risk of a court-ordered shutdown, which would impact its cash flow. Because of that uncertainty and the company's balance sheet issues, investors might want to wait for more clarity before buying. 

Phillips 66 Partners

Oil pipeline company Phillips 66 Partners (NYSE:PSXP) currently yields an enticing 12.7%. On the one hand, that payout seems sustainable since Phillips 66 Partners generates more than enough cash to cover that payout, and since it has a strong balance sheet with a low leverage ratio. However, it's also a co-owner of Energy Transfer's Dakota Access system. If that gets shut down, then Phillips 66 Partners might reduce its payout. It's better to watch this stock until there's clarity about the future of that pipeline and its cash flows.

Brookfield Property

Global real estate giant Brookfield Property (NASDAQ:BPY)(NASDAQ:BPYU) currently yields an eye-popping 11%. That's due to the COVID-19 headwinds facing its office, retail, and hospitality properties. Brookfield firmly believes that its pandemic-related woes will eventually fade, which is why it's using its strong balance sheet to maintain its payout. However, if problems persist, Brookfield Property might need to reduce its dividend so its financial profile doesn't deteriorate. 

ExxonMobil

Oil behemoth ExxonMobil (NYSE:XOM) currently yields 8%. It opted to maintain its dividend so far this year, even though a growing number of its peers have reduced theirs because of falling crude prices. Those lower oil prices forced the company to pile on debt to cover the payout and capital expenses. Borrowings rose from $46.9 billion to begin 2020 to $69.5 billion at the end of the second quarter. That's not a sustainable trend. Because of that, Exxon isn't an ideal dividend stock to buy right now, but it might be once again if crude prices (and the company's balance sheet) improve.

High yields with matching risk profiles

ONEOK, Energy Transfer, Brookfield Property, Phillips 66 Partners, and ExxonMobil all pay alluringly high yields. However, each payout has its issues. That's why yield-seeking investors should hold off on buying these stocks right now and instead consider putting them on their watch lists to see if those problems go away.